(Reland) Discard compositor frames from unloaded web content

content/renderer/render_widget.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_RENDERER_RENDER_WIDGET_H_
 #define CONTENT_RENDERER_RENDER_WIDGET_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 396 matching lines @@
 
   // When emulated, this returns original device scale factor.
   float GetOriginalDeviceScaleFactor() const;
 
   // Helper to convert |point| using ConvertWindowToViewport().
   gfx::Point ConvertWindowPointToViewport(const gfx::Point& point);
 
   virtual void TransferActiveWheelFlingAnimation(
       const blink::WebActiveWheelFlingParameters& params) {}
 
+  uint32_t GetContentSourceId();
+  void IncrementContentSourceId();
+
  protected:
   // Friend RefCounted so that the dtor can be non-public. Using this class
   // without ref-counting is an error.
   friend class base::RefCounted<RenderWidget>;
 
   // For unit tests.
   friend class RenderWidgetTest;
 
   enum ResizeAck {
     SEND_RESIZE_ACK,
@@ skipping 413 matching lines @@
   EditCommands edit_commands_;
 
   // This field stores drag/drop related info for the event that is currently
   // being handled. If the current event results in starting a drag/drop
   // session, this info is sent to the browser along with other drag/drop info.
   DragEventSourceInfo possible_drag_event_info_;
 
   bool time_to_first_active_paint_recorded_;
   base::TimeTicks was_shown_time_;
 
+  // This is initialized to zero and is incremented on each non-same-page
+  // navigation commit by RenderFrameImpl. At that time it is sent to the
+  // compositor so that it can tag compositor frames, and RenderFrameImpl is
+  // responsible for sending it to the browser process to be used to match
+  // each compositor frame to the most recent page navigation before it was
+  // generated.
+  // This only applies to main frames, and is not touched for subframe
+  // RenderWidgets, where there is no concern around displaying unloaded
+  // content.
+  // TODO(kenrb, fsamuel): This should be removed when SurfaceIDs can be used
+  // to replace it. See https://crbug.com/695579.
+  uint32_t current_content_source_id_;
+
   base::WeakPtrFactory<RenderWidget> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidget);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_RENDER_WIDGET_H_