Clear out pending SwapBufferComplete count when activating the compositor.

content/renderer/render_widget.cc

 // 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.
 
 #include "content/renderer/render_widget.h"
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/logging.h"
@@ skipping 1142 matching lines @@
     // OnSwapBuffersComplete.  So send a dummy message that will unblock the
     // browser's UI thread. This is not necessary on Mac, because SwapBuffers
     // now unblocks GetBackingStore on Mac.
     Send(new ViewHostMsg_UpdateIsDelayed(routing_id_));
   }
 #endif
 
   is_accelerated_compositing_active_ = true;
   Send(new ViewHostMsg_DidActivateAcceleratedCompositing(
       routing_id_, is_accelerated_compositing_active_));
+
+  // Ignore any swapbuffer complete callbacks corresponding
+  // to swapbuffer calls made before the compositor was activated.
+  num_swapbuffers_complete_pending_ = 0;
 }
 
 void RenderWidget::didDeactivateCompositor() {
   TRACE_EVENT0("gpu", "RenderWidget::didDeactivateCompositor");
 
   is_accelerated_compositing_active_ = false;
   Send(new ViewHostMsg_DidActivateAcceleratedCompositing(
       routing_id_, is_accelerated_compositing_active_));
 
   if (using_asynchronous_swapbuffers_)
@@ skipping 711 matching lines @@
   pending_smooth_scroll_gestures_.insert(std::make_pair(id, callback));
 }
 
 bool RenderWidget::WillHandleMouseEvent(const WebKit::WebMouseEvent& event) {
   return false;
 }
 
 bool RenderWidget::WebWidgetHandlesCompositorScheduling() const {
   return false;
 }