Discard compositor frames from unloaded web content

content/browser/renderer_host/render_widget_host_impl.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 313 matching lines @@
   // left on the existing timeouts.
   void StartHangMonitorTimeout(base::TimeDelta delay,
                                blink::WebInputEvent::Type event_type,
                                RendererUnresponsiveType hang_monitor_reason);
 
   // Stops all existing hang monitor timeouts and assumes the renderer is
   // responsive.
   void StopHangMonitorTimeout();
 
   // Starts the rendering timeout, which will clear displayed graphics if
-  // a new compositor frame is not received before it expires.
-  void StartNewContentRenderingTimeout();
+  // a new compositor frame is not received before it expires. This also causes
+  // any new compositor frames received with content_source_id less than
+  // |next_source_id| to be discarded.
+  void StartNewContentRenderingTimeout(uint32_t next_source_id);
 
   // Notification that a new compositor frame has been generated following
   // a page load. This stops |new_content_rendering_timeout_|, or prevents
   // the timer from running if the load commit message hasn't been received
   // yet.
   void OnFirstPaintAfterLoad();
 
   // Forwards the keyboard event with optional commands to the renderer. If
   // |key_event| is not forwarded for any reason, then |commands| are ignored.
   void ForwardKeyboardEventWithCommands(
@@ skipping 542 matching lines @@
   // Type of the last blocking event that started the hang monitor.
   blink::WebInputEvent::Type hang_monitor_event_type_;
 
   // Type of the last blocking event sent to the renderer.
   blink::WebInputEvent::Type last_event_type_;
 
   // This value indicates how long to wait for a new compositor frame from a
   // renderer process before clearing any previously displayed content.
   base::TimeDelta new_content_rendering_delay_;
 
+  // This identifier tags compositor frames according to the page load with
+  // which they are associated, to prevent an unloaded web page from being
+  // drawn after a navigation to a new page has already committed. This is

[danakj, 2017/03/01 18:14:28]

"This is be a"

[kenrb, 2017/03/02 17:08:17]

Done.

+  // be a no-op for non-top-level RenderWidgets, as that should always be
+  // zero.
+  // TODO(kenrb, fsamuel): We should use SurfaceIDs for this purpose when they
+  // are available in the renderer process. See https://crbug.com/695579.
+  uint32_t current_content_source_id_;
+
 #if defined(OS_MACOSX)
   std::unique_ptr<device::PowerSaveBlocker> power_save_blocker_;
 #endif
 
   base::WeakPtrFactory<RenderWidgetHostImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostImpl);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_IMPL_H_