add "view-painted" event to WebContent.

atom/browser/api/atom_api_web_contents.cc

@@ -733,6 +733,7 @@ bool WebContents::OnMessageReceived(const IPC::Message& message) {
     IPC_MESSAGE_HANDLER(AtomViewHostMsg_Message, OnRendererMessage)
     IPC_MESSAGE_HANDLER_DELAY_REPLY(AtomViewHostMsg_Message_Sync,
                                     OnRendererMessageSync)
+    IPC_MESSAGE_HANDLER(AtomViewHostMsg_DidCommitCompositorFrame, OnViewPainted)
     IPC_MESSAGE_HANDLER_CODE(ViewHostMsg_SetCursor, OnCursorChange,
       handled = false)
     IPC_MESSAGE_UNHANDLED(handled = false)
@@ -1298,6 +1299,10 @@ void WebContents::OnCursorChange(const content::WebCursor& cursor) {
   }
 }
 
+void WebContents::OnViewPainted() {
+  Emit("view-painted");
+}
+
 void WebContents::SetSize(const SetSizeParams& params) {
   if (guest_delegate_)
     guest_delegate_->SetSize(params);

atom/browser/api/atom_api_web_contents.h

@@ -294,6 +294,9 @@ class WebContents : public mate::TrackableObject<WebContents>,
                              const base::ListValue& args,
                              IPC::Message* message);
 
+  // Called when the hosted view gets graphical updates.
+  void OnViewPainted();
+
   v8::Global<v8::Value> session_;
   v8::Global<v8::Value> devtools_web_contents_;
   v8::Global<v8::Value> debugger_;

atom/common/api/api_messages.h

@@ -39,5 +39,7 @@ IPC_MESSAGE_ROUTED3(AtomViewMsg_Message,
 IPC_MESSAGE_ROUTED1(AtomViewHostMsg_UpdateDraggableRegions,
                     std::vector<atom::DraggableRegion> /* regions */)
 
+IPC_MESSAGE_ROUTED0(AtomViewHostMsg_DidCommitCompositorFrame)
+
 // Update renderer process preferences.
 IPC_MESSAGE_CONTROL1(AtomMsg_UpdatePreferences, base::ListValue)

atom/renderer/atom_render_view_observer.cc

@@ -141,6 +141,10 @@ void AtomRenderViewObserver::DraggableRegionsChanged(blink::WebFrame* frame) {
   Send(new AtomViewHostMsg_UpdateDraggableRegions(routing_id(), regions));
 }
 
+void AtomRenderViewObserver::DidCommitCompositorFrame() {
+  Send(new AtomViewHostMsg_DidCommitCompositorFrame(routing_id()));
+}
+
 bool AtomRenderViewObserver::OnMessageReceived(const IPC::Message& message) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(AtomRenderViewObserver, message)

atom/renderer/atom_render_view_observer.h

@@ -28,6 +28,7 @@ class AtomRenderViewObserver : public content::RenderViewObserver {
   // content::RenderViewObserver implementation.
   void DidCreateDocumentElement(blink::WebLocalFrame* frame) override;
   void DraggableRegionsChanged(blink::WebFrame* frame) override;
+  void DidCommitCompositorFrame() override;
   bool OnMessageReceived(const IPC::Message& message) override;
 
   void OnBrowserMessage(bool send_to_all,

docs/api/web-contents.md

@@ -448,6 +448,10 @@ app.on('ready', () => {
 })
 ```
 
+#### Event: 'view-painted'
+
+Emitted when a page's view is repainted.
+
 ### Instance Methods
 
 #### `contents.loadURL(url[, options])`