fix: Disable compositor recycling only for attached views (7-0-x) (#20846)

Backport of #20829

Notes: Fix flicker when switching between `BrowserView`s

patches/chromium/fix_disabling_compositor_recycling.patch

@@ -5,16 +5,20 @@ Subject: fix: disabling compositor recycling
 
 Compositor recycling is useful for Chrome because there can be many tabs and spinning up a compositor for each one would be costly. In practice, Chrome uses the parent compositor code path of browser_compositor_view_mac.mm; the NSView of each tab is detached when it's hidden and attached when it's shown. For Electron, there is no parent compositor, so we're forced into the "own compositor" code path, which seems to be non-optimal and pretty ruthless in terms of the release of resources. Electron has no real concept of multiple tabs per window, so it should be okay to disable this ruthless recycling altogether in Electron.
 
-diff --git a/content/browser/renderer_host/browser_compositor_view_mac.mm b/content/browser/renderer_host/browser_compositor_view_mac.mm
-index 18019d5794f688ca07b35a665cc9800bb1d3047a..60c7e980dd322ba012c564fca68848c3188ca5dc 100644
---- a/content/browser/renderer_host/browser_compositor_view_mac.mm
-+++ b/content/browser/renderer_host/browser_compositor_view_mac.mm
-@@ -209,7 +209,7 @@
- }
+diff --git a/content/browser/renderer_host/render_widget_host_view_mac.mm b/content/browser/renderer_host/render_widget_host_view_mac.mm
+index 7a3503fc687bc1877d8940cf6a3ec1bbeca83716..73bffbafcc664670dc14d5b6ee63f9e1e8b2e9fd 100644
+--- a/content/browser/renderer_host/render_widget_host_view_mac.mm
++++ b/content/browser/renderer_host/render_widget_host_view_mac.mm
+@@ -486,7 +486,11 @@
+     return;
  
- void BrowserCompositorMac::SetRenderWidgetHostIsHidden(bool hidden) {
--  render_widget_host_is_hidden_ = hidden;
-+  render_widget_host_is_hidden_ = false;
-   UpdateState();
+   host()->WasHidden();
+-  browser_compositor_->SetRenderWidgetHostIsHidden(true);
++  // Consider the RWHV occluded only if it is not attached to a window
++  // (e.g. unattached BrowserView). Otherwise we treat it as visible to
++  // prevent unnecessary compositor recycling.
++  const bool unattached = ![GetInProcessNSView() window];
++  browser_compositor_->SetRenderWidgetHostIsHidden(unattached);
  }
  
+ void RenderWidgetHostViewMac::SetSize(const gfx::Size& size) {