Make WindowReachedScreen support async readback

content/browser/renderer_host/render_widget_host_impl.h

Index: content/browser/renderer_host/render_widget_host_impl.h
diff --git a/content/browser/renderer_host/render_widget_host_impl.h b/content/browser/renderer_host/render_widget_host_impl.h
index 94a42ff3af2523563314c8937173dbe11ef88e3e..4b595698cce7c6d251b940d6756d580fc8bc0e7b 100644
--- a/content/browser/renderer_host/render_widget_host_impl.h
+++ b/content/browser/renderer_host/render_widget_host_impl.h
@@ -547,6 +547,12 @@ class CONTENT_EXPORT RenderWidgetHostImpl : virtual public RenderWidgetHost,
   // Don't check whether we expected a resize ack during layout tests.
   static void DisableResizeAckCheckForTesting();
 
+  void WindowSnapshotAsyncCallback(
+      int routing_id,
+      int snapshot_id,
+      gfx::Size snapshot_size,
+      scoped_refptr<base::RefCountedBytes> png_data);
+
  protected:
   virtual RenderWidgetHostImpl* AsRenderWidgetHostImpl() OVERRIDE;