Fix race conditions in window snapshot code.

content/renderer/render_widget.h

Index: content/renderer/render_widget.h
diff --git a/content/renderer/render_widget.h b/content/renderer/render_widget.h
index 8341b0aadaeef7b59af64c9a29eee6e12709bf17..39870645e3f78be7ce68563f2ed1a442aba7c3e5 100644
--- a/content/renderer/render_widget.h
+++ b/content/renderer/render_widget.h
@@ -241,6 +241,8 @@ class CONTENT_EXPORT RenderWidget
   void DisableScreenMetricsEmulation();
   void SetPopupOriginAdjustmentsForEmulation(ScreenMetricsEmulator* emulator);
 
+  void ScheduleCompositeWithForcedRedraw();
+
  protected:
   // Friend RefCounted so that the dtor can be non-public. Using this class
   // without ref-counting is an error.
@@ -547,6 +549,8 @@ class CONTENT_EXPORT RenderWidget
 
   bool OnSnapshotHelper(const gfx::Rect& src_subrect, SkBitmap* bitmap);
 
+  void ScheduleCompositeImpl(bool force_redraw);
+
   // Routing ID that allows us to communicate to the parent browser process
   // RenderWidgetHost. When MSG_ROUTING_NONE, no messages may be sent.
   int32 routing_id_;