Use observer pattern instead of sniffing SwapCompositorFrame IPC

content/browser/renderer_host/render_widget_host_delegate.h

Index: content/browser/renderer_host/render_widget_host_delegate.h
diff --git a/content/browser/renderer_host/render_widget_host_delegate.h b/content/browser/renderer_host/render_widget_host_delegate.h
index abea25d83ac4ed8f4a0e4babce94e7742134cd0a..a2d2d9bcfe55b03617deab88d9a8c5a6ea9a36dd 100644
--- a/content/browser/renderer_host/render_widget_host_delegate.h
+++ b/content/browser/renderer_host/render_widget_host_delegate.h
@@ -249,6 +249,9 @@ class CONTENT_EXPORT RenderWidgetHostDelegate {
   // not a WebContents, returns nullptr.
   virtual WebContents* GetAsWebContents();
 
+  // Notifies that a CompositorFrame was received from the renderer.
+  virtual void DidReceiveCompositorFrame() {}
+
  protected:
   virtual ~RenderWidgetHostDelegate() {}
 };