feat: Add option to conditionally disable site instance patches (#18554)

* feat: Add option to conditionally disable site instance patches (#18396)

* chore: allow conditional disable of the site instance override patches at runtime

* feat: add app.allowRendererProcessReuse property to allow runtime disable of site instance overrides

spec: add tests for the new allowRendererProcessReuse property

feat: add console warnings / errors for loading non context-aware native modules
  * Only error if the patch is disabled
  * Warn all the time, this will ship in Electron 7

* chore: do not warn in about context aware in v6

* chore: update patches

DEPS

@@ -12,7 +12,7 @@ vars = {
   'chromium_version':
     '76.0.3809.23',
   'node_version':
-    'a86a4a160dc520c61a602c949a32a1bc4c0fc633',
+    'dee0db9864a001ffc16440f725f4952a1a417069',
 
   'boto_version': 'f7574aa6cc2c819430c1f05e9a1a1a666ef8169b',
   'pyyaml_version': '3.12',

atom/browser/api/atom_api_app.cc

@@ -1279,6 +1279,13 @@ std::string App::GetUserAgentFallback() {
   return AtomBrowserClient::Get()->GetUserAgent();
 }
 
+void App::SetBrowserClientCanUseCustomSiteInstance(bool should_disable) {
+  AtomBrowserClient::Get()->SetCanUseCustomSiteInstance(should_disable);
+}
+bool App::CanBrowserClientUseCustomSiteInstance() {
+  return AtomBrowserClient::Get()->CanUseCustomSiteInstance();
+}
+
 #if defined(OS_MACOSX)
 bool App::MoveToApplicationsFolder(mate::Arguments* args) {
   return ui::cocoa::AtomBundleMover::Move(args);
@@ -1441,7 +1448,10 @@ void App::BuildPrototype(v8::Isolate* isolate,
 #endif
       .SetProperty("userAgentFallback", &App::GetUserAgentFallback,
                    &App::SetUserAgentFallback)
-      .SetMethod("enableSandbox", &App::EnableSandbox);
+      .SetMethod("enableSandbox", &App::EnableSandbox)
+      .SetProperty("allowRendererProcessReuse",
+                   &App::CanBrowserClientUseCustomSiteInstance,
+                   &App::SetBrowserClientCanUseCustomSiteInstance);
 }
 
 }  // namespace api

atom/browser/api/atom_api_app.h

@@ -212,6 +212,8 @@ class App : public AtomBrowserClient::Delegate,
   void EnableSandbox(mate::Arguments* args);
   void SetUserAgentFallback(const std::string& user_agent);
   std::string GetUserAgentFallback();
+  void SetBrowserClientCanUseCustomSiteInstance(bool should_disable);
+  bool CanBrowserClientUseCustomSiteInstance();
 
 #if defined(OS_MACOSX)
   bool MoveToApplicationsFolder(mate::Arguments* args);

atom/browser/atom_browser_client.cc

@@ -397,6 +397,14 @@ void AtomBrowserClient::OverrideWebkitPrefs(content::RenderViewHost* host,
     web_preferences->OverrideWebkitPrefs(prefs);
 }
 
+void AtomBrowserClient::SetCanUseCustomSiteInstance(bool should_disable) {
+  disable_process_restart_tricks_ = should_disable;
+}
+
+bool AtomBrowserClient::CanUseCustomSiteInstance() {
+  return disable_process_restart_tricks_;
+}
+
 content::ContentBrowserClient::SiteInstanceForNavigationType
 AtomBrowserClient::ShouldOverrideSiteInstanceForNavigation(
     content::RenderFrameHost* current_rfh,
@@ -503,6 +511,10 @@ void AtomBrowserClient::AppendExtraCommandLineSwitches(
       web_preferences->AppendCommandLineSwitches(command_line);
     SessionPreferences::AppendExtraCommandLineSwitches(
         web_contents->GetBrowserContext(), command_line);
+    if (CanUseCustomSiteInstance()) {
+      command_line->AppendSwitch(
+          switches::kDisableElectronSiteInstanceOverrides);
+    }
   }
 }
 

atom/browser/atom_browser_client.h

@@ -67,6 +67,9 @@ class AtomBrowserClient : public content::ContentBrowserClient,
   std::string GetUserAgent() const override;
   void SetUserAgent(const std::string& user_agent);
 
+  void SetCanUseCustomSiteInstance(bool should_disable);
+  bool CanUseCustomSiteInstance() override;
+
  protected:
   void RenderProcessWillLaunch(
       content::RenderProcessHost* host,
@@ -234,6 +237,8 @@ class AtomBrowserClient : public content::ContentBrowserClient,
 
   std::string user_agent_override_ = "";
 
+  bool disable_process_restart_tricks_ = false;
+
   DISALLOW_COPY_AND_ASSIGN(AtomBrowserClient);
 };
 

atom/common/options_switches.cc

@@ -232,6 +232,8 @@ const char kScrollBounce[] = "scroll-bounce";
 const char kHiddenPage[] = "hidden-page";
 const char kNativeWindowOpen[] = "native-window-open";
 const char kWebviewTag[] = "webview-tag";
+const char kDisableElectronSiteInstanceOverrides[] =
+    "disable-electron-site-instance-overrides";
 
 // Command switch passed to renderer process to control nodeIntegration.
 const char kNodeIntegrationInWorker[] = "node-integration-in-worker";

atom/common/options_switches.h

@@ -118,6 +118,7 @@ extern const char kNodeIntegrationInWorker[];
 extern const char kWebviewTag[];
 extern const char kNodeIntegrationInSubFrames[];
 extern const char kDisableHtmlFullscreenWindowResize[];
+extern const char kDisableElectronSiteInstanceOverrides[];
 
 extern const char kWidevineCdmPath[];
 extern const char kWidevineCdmVersion[];

atom/renderer/atom_renderer_client.cc

@@ -103,6 +103,12 @@ void AtomRendererClient::DidCreateScriptContext(
 
   // Setup node environment for each window.
   node::Environment* env = node_bindings_->CreateEnvironment(context);
+  auto* command_line = base::CommandLine::ForCurrentProcess();
+  // If we have disabled the site instance overrides we should prevent loading
+  // any non-context aware native module
+  if (command_line->HasSwitch(switches::kDisableElectronSiteInstanceOverrides))
+    env->ForceOnlyContextAwareNativeModules();
+
   environments_.insert(env);
 
   // Add Electron extended APIs.
@@ -144,9 +150,11 @@ void AtomRendererClient::WillReleaseScriptContext(
   // Destroy the node environment.  We only do this if node support has been
   // enabled for sub-frames to avoid a change-of-behavior / introduce crashes
   // for existing users.
-  // TODO(MarshallOfSOund): Free the environment regardless of this switch
-  if (base::CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kNodeIntegrationInSubFrames))
+  // We also do this if we have disable electron site instance overrides to
+  // avoid memory leaks
+  auto* command_line = base::CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kNodeIntegrationInSubFrames) ||
+      command_line->HasSwitch(switches::kDisableElectronSiteInstanceOverrides))
     node::FreeEnvironment(env);
 
   // ElectronBindings is tracking node environments.

docs/api/app.md

@@ -1386,3 +1386,16 @@ A `Boolean` property that returns  `true` if the app is packaged, `false` otherw
 [Squirrel-Windows]: https://github.com/Squirrel/Squirrel.Windows
 [JumpListBeginListMSDN]: https://msdn.microsoft.com/en-us/library/windows/desktop/dd378398(v=vs.85).aspx
 [about-panel-options]: https://developer.apple.com/reference/appkit/nsapplication/1428479-orderfrontstandardaboutpanelwith?language=objc
+
+### `app.allowRendererProcessReuse`
+
+A `Boolean` which when `true` disables the overrides that Electron has in place
+to ensure renderer processes are restarted on every navigation.  The current
+default value for this property is `false`.
+
+The intention is for these overrides to become disabled by default and then at
+some point in the future this property will be removed.  This property impacts
+which native modules you can use in the renderer process.  For more information
+on the direction Electron is going with renderer process restarts and usage of
+native modules in the renderer process please check out this
+[Tracking Issue](https://github.com/electron/electron/issues/18397).

patches/common/chromium/.patches

@@ -9,7 +9,6 @@ browser_compositor_mac.patch
 can_create_window.patch
 disable_hidden.patch
 dom_storage_limits.patch
-frame_host_manager.patch
 out_of_process_instance.patch
 render_widget_host_view_base.patch
 render_widget_host_view_mac.patch
@@ -59,7 +58,6 @@ command-ismediakey.patch
 tts.patch
 printing.patch
 verbose_generate_breakpad_symbols.patch
-cross_site_document_resource_handler.patch
 content_allow_embedder_to_prevent_locking_scheme_registry.patch
 support_mixed_sandbox_with_zygote.patch
 disable_color_correct_rendering.patch
@@ -80,3 +78,5 @@ partially_revert_fb4ab3be3fc0024d00358d5b7816d3215a8ff20c.patch
 disable_custom_libcxx_on_windows.patch
 fix_breakpad_symbol_generation_on_linux_arm.patch
 woa_compiler_workaround.patch
+cross_site_document_resource_handler.patch
+frame_host_manager.patch

patches/common/chromium/blink_local_frame.patch

@@ -14,7 +14,7 @@ when there is code doing that.
 This patch reverts the change to fix the crash in Electron.
 
 diff --git a/third_party/blink/renderer/core/frame/local_frame.cc b/third_party/blink/renderer/core/frame/local_frame.cc
-index 4851cb4a227b8cbccfb0775d46f1ea001e5fce74..8f24199a056eac92ba7f2173fb1c7f173d50d6ff 100644
+index 06f9c9f62dc94bd093942d9ee523a4279203a177..3ee1caa9ad92cfedd326b364817ce9b5e8db800e 100644
 --- a/third_party/blink/renderer/core/frame/local_frame.cc
 +++ b/third_party/blink/renderer/core/frame/local_frame.cc
 @@ -393,10 +393,6 @@ void LocalFrame::DetachImpl(FrameDetachType type) {

patches/common/chromium/can_create_window.patch

@@ -5,10 +5,10 @@ Subject: can_create_window.patch
 
 
 diff --git a/content/browser/frame_host/render_frame_host_impl.cc b/content/browser/frame_host/render_frame_host_impl.cc
-index ae459238a1bd31e219f1b1a2cb539d4c071dcf33..63e11474acb2af5406015b7a3d39dc51cf160506 100644
+index b07b5f0b6eddfb9c754bed039c061de98a361f0e..4d1f8c2c5499291f55bf17cd7a0f45c3655c2985 100644
 --- a/content/browser/frame_host/render_frame_host_impl.cc
 +++ b/content/browser/frame_host/render_frame_host_impl.cc
-@@ -3709,6 +3709,7 @@ void RenderFrameHostImpl::CreateNewWindow(
+@@ -3712,6 +3712,7 @@ void RenderFrameHostImpl::CreateNewWindow(
            last_committed_origin_, params->window_container_type,
            params->target_url, params->referrer.To<Referrer>(),
            params->frame_name, params->disposition, *params->features,
@@ -17,10 +17,10 @@ index ae459238a1bd31e219f1b1a2cb539d4c071dcf33..63e11474acb2af5406015b7a3d39dc51
            &no_javascript_access);
  
 diff --git a/content/common/frame.mojom b/content/common/frame.mojom
-index 82882159b0bac6d47d678c485de0aacc7db06c2d..dd2299094b79d82da7ec1cd8f559050b6f0e2af5 100644
+index 577fd09ef05584962b5357028702d54f36719c6a..6dd3dcb250a5744d62b13b0ee5544d8270d8d882 100644
 --- a/content/common/frame.mojom
 +++ b/content/common/frame.mojom
-@@ -291,6 +291,10 @@ struct CreateNewWindowParams {
+@@ -298,6 +298,10 @@ struct CreateNewWindowParams {
  
    // The window features to use for the new window.
    blink.mojom.WindowFeatures features;

patches/common/chromium/cross_site_document_resource_handler.patch

@@ -22,31 +22,31 @@ index d514c10160dd12f225c42e927977660cacbc9c43..49345f1d4d75c8b96efe485202d89774
  }
  
 diff --git a/content/public/browser/content_browser_client.cc b/content/public/browser/content_browser_client.cc
-index 671d2259d50bfbb5b56a79907c1c86218ee04469..373eee0faf29f2d4be98156f4abd476c61dff713 100644
+index d15061de5254fd4f248fed92f47a1b1fcf34cd68..ac0151af07e440b7e4b7a291530abe108b5cd7d9 100644
 --- a/content/public/browser/content_browser_client.cc
 +++ b/content/public/browser/content_browser_client.cc
-@@ -62,6 +62,10 @@ ContentBrowserClient::SiteInstanceForNavigationType ContentBrowserClient::Should
-   return SiteInstanceForNavigationType::ASK_CHROMIUM;
+@@ -57,6 +57,10 @@ std::unique_ptr<BrowserMainParts> ContentBrowserClient::CreateBrowserMainParts(
+   return nullptr;
  }
  
 +bool ContentBrowserClient::ShouldBypassCORB(int render_process_id) const {
 +  return false;
 +}
 +
- std::unique_ptr<BrowserMainParts> ContentBrowserClient::CreateBrowserMainParts(
-     const MainFunctionParams& parameters) {
-   return nullptr;
+ void ContentBrowserClient::PostAfterStartupTask(
+     const base::Location& from_here,
+     const scoped_refptr<base::TaskRunner>& task_runner,
 diff --git a/content/public/browser/content_browser_client.h b/content/public/browser/content_browser_client.h
-index fcc5a0e5cd830afe459c1defe968b01e3f05f764..3067cf61e02f6abd048dc888237ef9e2d4909a78 100644
+index e5cddbc3a28e0f90bd1d1ae6ebe28d5f2d0299c7..93fd647a472466633d608e05c0b66653c696073d 100644
 --- a/content/public/browser/content_browser_client.h
 +++ b/content/public/browser/content_browser_client.h
-@@ -242,6 +242,9 @@ class CONTENT_EXPORT ContentBrowserClient {
-       content::RenderFrameHost* rfh,
-       content::SiteInstance* pending_site_instance) {}
+@@ -219,6 +219,9 @@ class CONTENT_EXPORT ContentBrowserClient {
+   virtual std::unique_ptr<BrowserMainParts> CreateBrowserMainParts(
+       const MainFunctionParams& parameters);
  
 +  // Electron: Allows bypassing CORB checks for a renderer process.
 +  virtual bool ShouldBypassCORB(int render_process_id) const;
 +
-   // Allows the embedder to set any number of custom BrowserMainParts
-   // implementations for the browser startup code. See comments in
-   // browser_main_parts.h.
+   // Allows the embedder to change the default behavior of
+   // BrowserThread::PostAfterStartupTask to better match whatever
+   // definition of "startup" the embedder has in mind. This may be

patches/common/chromium/frame_host_manager.patch

@@ -4,7 +4,8 @@ Date: Wed, 14 Nov 2018 20:38:46 +0530
 Subject: frame_host_manager.patch
 
 Allows embedder to intercept site instances chosen by chromium
-and respond with custom instance.
+and respond with custom instance. Also allows for us to at-runtime
+enable or disable this patch.
 
 diff --git a/content/browser/browsing_instance.cc b/content/browser/browsing_instance.cc
 index 12e1c5cff95aa6d0a907a249208e23371cf29785..e64703c0edac7f7e9af211b0130a776e6ce3f953 100644
@@ -41,91 +42,100 @@ index 775b64a8d20f89845812852a2904a1e6875c2b4a..5235b57bbf44fc7b30ca6943c43a290f
    // another SiteInstance for the same site.
    void RegisterSiteInstance(SiteInstanceImpl* site_instance);
 diff --git a/content/browser/frame_host/render_frame_host_manager.cc b/content/browser/frame_host/render_frame_host_manager.cc
-index 297b61198dd46114b3d8c89488a71ed01aa299c4..1f0ec6c02e8b189c9170441e2c8709cc1b561c84 100644
+index 297b61198dd46114b3d8c89488a71ed01aa299c4..40b848a8b448bed2d167bf5f6c0f25971b603ed2 100644
 --- a/content/browser/frame_host/render_frame_host_manager.cc
 +++ b/content/browser/frame_host/render_frame_host_manager.cc
-@@ -2127,6 +2127,16 @@ bool RenderFrameHostManager::InitRenderView(
+@@ -2127,6 +2127,20 @@ bool RenderFrameHostManager::InitRenderView(
  scoped_refptr<SiteInstance>
  RenderFrameHostManager::GetSiteInstanceForNavigationRequest(
      const NavigationRequest& request) {
-+  BrowserContext* browser_context =
-+      delegate_->GetControllerForRenderManager().GetBrowserContext();
-+  // If the navigation can swap SiteInstances, compute the SiteInstance it
-+  // should use.
-+  // TODO(clamy): We should also consider as a candidate SiteInstance the
-+  // speculative SiteInstance that was computed on redirects.
-+  scoped_refptr<SiteInstance> candidate_site_instance =
-+      speculative_render_frame_host_
-+          ? speculative_render_frame_host_->GetSiteInstance()
-+          : nullptr;
++  BrowserContext* browser_context = nullptr;
++  scoped_refptr<SiteInstance> candidate_site_instance;
++  if (!GetContentClient()->browser()->CanUseCustomSiteInstance()) {
++    browser_context =
++        delegate_->GetControllerForRenderManager().GetBrowserContext();
++    // If the navigation can swap SiteInstances, compute the SiteInstance it
++    // should use.
++    // TODO(clamy): We should also consider as a candidate SiteInstance the
++    // speculative SiteInstance that was computed on redirects.
++    candidate_site_instance =
++        speculative_render_frame_host_
++            ? speculative_render_frame_host_->GetSiteInstance()
++            : nullptr;
++  }
    // First, check if the navigation can switch SiteInstances. If not, the
    // navigation should use the current SiteInstance.
    SiteInstance* current_site_instance = render_frame_host_->GetSiteInstance();
-@@ -2158,6 +2168,51 @@ RenderFrameHostManager::GetSiteInstanceForNavigationRequest(
+@@ -2158,6 +2172,53 @@ RenderFrameHostManager::GetSiteInstanceForNavigationRequest(
                                                request.common_params().url);
      no_renderer_swap_allowed |=
          request.from_begin_navigation() && !can_renderer_initiate_transfer;
 +
-+    bool has_response_started =
-+        (request.state() == NavigationRequest::RESPONSE_STARTED ||
-+         request.state() == NavigationRequest::FAILED) &&
-+        !speculative_render_frame_host_;
-+    // Gives user a chance to choose a custom site instance.
-+    SiteInstance* affinity_site_instance = nullptr;
-+    scoped_refptr<SiteInstance> overriden_site_instance;
-+    ContentBrowserClient::SiteInstanceForNavigationType siteInstanceType =
-+        GetContentClient()->browser()->ShouldOverrideSiteInstanceForNavigation(
-+            current_frame_host(), speculative_frame_host(), browser_context,
-+            request.common_params().url, has_response_started,
-+            &affinity_site_instance);
-+    switch (siteInstanceType) {
-+      case ContentBrowserClient::SiteInstanceForNavigationType::
-+          FORCE_CANDIDATE_OR_NEW:
-+        overriden_site_instance =
-+            candidate_site_instance
-+                ? candidate_site_instance
-+                : current_site_instance->CreateRelatedSiteInstance(
-+                                             request.common_params().url);
-+        break;
-+      case ContentBrowserClient::SiteInstanceForNavigationType::FORCE_CURRENT:
-+        overriden_site_instance = render_frame_host_->GetSiteInstance();
-+        break;
-+      case ContentBrowserClient::SiteInstanceForNavigationType::FORCE_AFFINITY:
-+        DCHECK(affinity_site_instance);
-+        overriden_site_instance =
-+            scoped_refptr<SiteInstance>(affinity_site_instance);
-+        break;
-+      case ContentBrowserClient::SiteInstanceForNavigationType::ASK_CHROMIUM:
-+        DCHECK(!affinity_site_instance);
-+        break;
-+      default:
-+        break;
-+    }
-+    if (overriden_site_instance) {
-+      if (siteInstanceType ==
-+          ContentBrowserClient::SiteInstanceForNavigationType::
-+              FORCE_CANDIDATE_OR_NEW) {
-+        GetContentClient()->browser()->RegisterPendingSiteInstance(
-+            render_frame_host_.get(), overriden_site_instance.get());
++    if (!GetContentClient()->browser()->CanUseCustomSiteInstance()) {
++      bool has_response_started =
++          (request.state() == NavigationRequest::RESPONSE_STARTED ||
++          request.state() == NavigationRequest::FAILED) &&
++          !speculative_render_frame_host_;
++      // Gives user a chance to choose a custom site instance.
++      SiteInstance* affinity_site_instance = nullptr;
++      scoped_refptr<SiteInstance> overriden_site_instance;
++      ContentBrowserClient::SiteInstanceForNavigationType siteInstanceType =
++          GetContentClient()->browser()->ShouldOverrideSiteInstanceForNavigation(
++              current_frame_host(), speculative_frame_host(), browser_context,
++              request.common_params().url, has_response_started,
++              &affinity_site_instance);
++      switch (siteInstanceType) {
++        case ContentBrowserClient::SiteInstanceForNavigationType::
++            FORCE_CANDIDATE_OR_NEW:
++          overriden_site_instance =
++              candidate_site_instance
++                  ? candidate_site_instance
++                  : current_site_instance->CreateRelatedSiteInstance(
++                                              request.common_params().url);
++          break;
++        case ContentBrowserClient::SiteInstanceForNavigationType::FORCE_CURRENT:
++          overriden_site_instance = render_frame_host_->GetSiteInstance();
++          break;
++        case ContentBrowserClient::SiteInstanceForNavigationType::FORCE_AFFINITY:
++          DCHECK(affinity_site_instance);
++          overriden_site_instance =
++              scoped_refptr<SiteInstance>(affinity_site_instance);
++          break;
++        case ContentBrowserClient::SiteInstanceForNavigationType::ASK_CHROMIUM:
++          DCHECK(!affinity_site_instance);
++          break;
++        default:
++          break;
++      }
++      if (overriden_site_instance) {
++        if (siteInstanceType ==
++            ContentBrowserClient::SiteInstanceForNavigationType::
++                FORCE_CANDIDATE_OR_NEW) {
++          GetContentClient()->browser()->RegisterPendingSiteInstance(
++              render_frame_host_.get(), overriden_site_instance.get());
++        }
++        return overriden_site_instance;
 +      }
-+      return overriden_site_instance;
 +    }
    } else {
      // Subframe navigations will use the current renderer, unless specifically
      // allowed to swap processes.
-@@ -2169,23 +2224,17 @@ RenderFrameHostManager::GetSiteInstanceForNavigationRequest(
+@@ -2169,23 +2230,28 @@ RenderFrameHostManager::GetSiteInstanceForNavigationRequest(
    if (no_renderer_swap_allowed && !should_swap_for_error_isolation)
      return scoped_refptr<SiteInstance>(current_site_instance);
  
--  // If the navigation can swap SiteInstances, compute the SiteInstance it
--  // should use.
--  // TODO(clamy): We should also consider as a candidate SiteInstance the
--  // speculative SiteInstance that was computed on redirects.
++  if (GetContentClient()->browser()->CanUseCustomSiteInstance()) {
+   // If the navigation can swap SiteInstances, compute the SiteInstance it
+   // should use.
+   // TODO(clamy): We should also consider as a candidate SiteInstance the
+   // speculative SiteInstance that was computed on redirects.
 -  SiteInstance* candidate_site_instance =
--      speculative_render_frame_host_
--          ? speculative_render_frame_host_->GetSiteInstance()
--          : nullptr;
--
++  candidate_site_instance =
+       speculative_render_frame_host_
+           ? speculative_render_frame_host_->GetSiteInstance()
+           : nullptr;
++  }
+ 
    scoped_refptr<SiteInstance> dest_site_instance = GetSiteInstanceForNavigation(
        request.common_params().url, request.source_site_instance(),
 -      request.dest_site_instance(), candidate_site_instance,
@@ -169,13 +179,17 @@ index a46901055bdf17b6b0dab14edf753b234dc04a12..29c201b0c95eb0c7a35f47d6f3ab5b48
    size_t GetRelatedActiveContentsCount() override;
    bool RequiresDedicatedProcess() override;
 diff --git a/content/public/browser/content_browser_client.cc b/content/public/browser/content_browser_client.cc
-index d15061de5254fd4f248fed92f47a1b1fcf34cd68..671d2259d50bfbb5b56a79907c1c86218ee04469 100644
+index ac0151af07e440b7e4b7a291530abe108b5cd7d9..f40a4ff5f08e906e62dd838eb5af63ade92037d2 100644
 --- a/content/public/browser/content_browser_client.cc
 +++ b/content/public/browser/content_browser_client.cc
-@@ -52,6 +52,16 @@ void OverrideOnBindInterface(const service_manager::BindSourceInfo& remote_info,
+@@ -52,6 +52,20 @@ void OverrideOnBindInterface(const service_manager::BindSourceInfo& remote_info,
                                                           handle);
  }
  
++bool ContentBrowserClient::CanUseCustomSiteInstance() {
++  return false;
++}
++
 +ContentBrowserClient::SiteInstanceForNavigationType ContentBrowserClient::ShouldOverrideSiteInstanceForNavigation(
 +    content::RenderFrameHost* current_rfh,
 +    content::RenderFrameHost* speculative_rfh,
@@ -190,10 +204,10 @@ index d15061de5254fd4f248fed92f47a1b1fcf34cd68..671d2259d50bfbb5b56a79907c1c8621
      const MainFunctionParams& parameters) {
    return nullptr;
 diff --git a/content/public/browser/content_browser_client.h b/content/public/browser/content_browser_client.h
-index e5cddbc3a28e0f90bd1d1ae6ebe28d5f2d0299c7..fcc5a0e5cd830afe459c1defe968b01e3f05f764 100644
+index 93fd647a472466633d608e05c0b66653c696073d..a179e37db44e67143d63af2746e43b8231b30b17 100644
 --- a/content/public/browser/content_browser_client.h
 +++ b/content/public/browser/content_browser_client.h
-@@ -211,8 +211,37 @@ CONTENT_EXPORT void OverrideOnBindInterface(
+@@ -211,8 +211,40 @@ CONTENT_EXPORT void OverrideOnBindInterface(
  // the observer interfaces.)
  class CONTENT_EXPORT ContentBrowserClient {
   public:
@@ -214,6 +228,9 @@ index e5cddbc3a28e0f90bd1d1ae6ebe28d5f2d0299c7..fcc5a0e5cd830afe459c1defe968b01e
 +  };
    virtual ~ContentBrowserClient() {}
  
++  // Electron: Allows disabling the below ShouldOverride patch
++  virtual bool CanUseCustomSiteInstance();
++
 +  // Electron: Allows overriding the SiteInstance when navigating.
 +  virtual SiteInstanceForNavigationType ShouldOverrideSiteInstanceForNavigation(
 +    content::RenderFrameHost* current_rfh,

patches/common/chromium/woa_compiler_workaround.patch

@@ -19,7 +19,7 @@ index 082dc5ec7ac304109a267456df4660c2cfa672f9..a4b14a8dddb02a9bd3ac7a0967ae6c4c
 @@ -40,6 +40,11 @@ CLANG_REVISION = '67510fac36d27b2e22c7cd955fc167136b737b93'
  CLANG_SVN_REVISION = '361212'
  CLANG_SUB_REVISION = 4
-
+ 
 +if os.getenv("ELECTRON_BUILDING_WOA"):
 +    CLANG_REVISION = '56bee1a90a71876cb5067b108bf5715fa1c4e843'
 +    CLANG_SVN_REVISION = '361657'

spec-main/api-app-spec.ts

@@ -1369,6 +1369,26 @@ describe('default behavior', () => {
       expect(app.userAgentFallback).to.equal(initialValue)
     })
   })
+
+  describe('app.allowRendererProcessReuse', () => {
+    it('should default to false', () => {
+      expect(app.allowRendererProcessReuse).to.equal(false)
+    })
+
+    it('should cause renderer processes to get new PIDs when false', async () => {
+      const output = await runTestApp('site-instance-overrides', 'false')
+      expect(output[0]).to.be.a('number').that.is.greaterThan(0)
+      expect(output[1]).to.be.a('number').that.is.greaterThan(0)
+      expect(output[0]).to.not.equal(output[1])
+    })
+
+    it('should cause renderer processes to keep the same PID when true', async () => {
+      const output = await runTestApp('site-instance-overrides', 'true')
+      expect(output[0]).to.be.a('number').that.is.greaterThan(0)
+      expect(output[1]).to.be.a('number').that.is.greaterThan(0)
+      expect(output[0]).to.equal(output[1])
+    })
+  })
 })
 
 async function runTestApp (name: string, ...args: any[]) {

spec/fixtures/api/site-instance-overrides/index.html

@@ -0,0 +1 @@
+<html></html>

spec/fixtures/api/site-instance-overrides/main.js

@@ -0,0 +1,33 @@
+const { app, BrowserWindow, ipcMain } = require('electron')
+const path = require('path')
+
+process.on('uncaughtException', (e) => {
+  console.error(e)
+  process.exit(1)
+})
+
+app.allowRendererProcessReuse = JSON.parse(process.argv[2])
+
+const pids = []
+let win
+
+ipcMain.on('pid', (event, pid) => {
+  pids.push(pid)
+  if (pids.length === 2) {
+    console.log(JSON.stringify(pids))
+    if (win) win.close()
+    app.quit()
+  } else {
+    if (win) win.reload()
+  }
+})
+
+app.whenReady().then(() => {
+  win = new BrowserWindow({
+    show: false,
+    webPreferences: {
+      preload: path.resolve(__dirname, 'preload.js')
+    }
+  })
+  win.loadFile('index.html')
+})

spec/fixtures/api/site-instance-overrides/package.json

@@ -0,0 +1,4 @@
+{
+  "name": "site-instance-overrides",
+  "main": "main.js"
+}

spec/fixtures/api/site-instance-overrides/preload.js

@@ -0,0 +1,3 @@
+const { ipcRenderer } = require('electron')
+
+ipcRenderer.send('pid', process.pid)