Fix race conditions in window snapshot code.

content/renderer/gpu/render_widget_compositor.h

Index: content/renderer/gpu/render_widget_compositor.h
diff --git a/content/renderer/gpu/render_widget_compositor.h b/content/renderer/gpu/render_widget_compositor.h
index 060d0b85e9ee9b0574e796b4025df181651766d1..46d886d5b6a6cb9e16f50574ec9ecbc96eaf747f 100644
--- a/content/renderer/gpu/render_widget_compositor.h
+++ b/content/renderer/gpu/render_widget_compositor.h
@@ -54,6 +54,9 @@ class RenderWidgetCompositor : public WebKit::WebLayerTreeView,
   int GetLayerTreeId() const;
   void NotifyInputThrottledUntilCommit();
   const cc::Layer* GetRootLayer() const;
+  // Like setNeedsRedraw, but forces the frame to be drawn, without
+  // any early-outs.

[jamesr, 2013/10/02 00:06:41]

is this the same as SetNeedsRedrawRect(...)? i.e., force window damage?  If it's
not, could you explain in the comment how it's different?  This function should
be next to that in the header since the two are closely related

+  void SetNeedsForcedRedraw();
 
   // WebLayerTreeView implementation.
   virtual void setSurfaceReady();