Support browser side thumbnailing for GPU composited pages on Windows.

content/port/browser/render_widget_host_view_port.h

Index: content/port/browser/render_widget_host_view_port.h
diff --git a/content/port/browser/render_widget_host_view_port.h b/content/port/browser/render_widget_host_view_port.h
index 471c4273f559b0090afe9550cd0df7709687fa93..7d84000cb6b551589d192079f6c90b0ad4c0579d 100644
--- a/content/port/browser/render_widget_host_view_port.h
+++ b/content/port/browser/render_widget_host_view_port.h
@@ -138,6 +138,12 @@ class CONTENT_EXPORT RenderWidgetHostViewPort : public RenderWidgetHostView {
   // Allocate a backing store for this view.
   virtual BackingStore* AllocBackingStore(const gfx::Size& size) = 0;
 
+  // Copies the contents of the compositing surface into the given
+  // (uninitialized) PlatformCanvas if any. Returns true on success, false
+  // otherwise.
+  virtual bool CopyFromCompositingSurface(const gfx::Size& size,
+                                          skia::PlatformCanvas* output) = 0;
+
   // Called when accelerated compositing state changes.
   virtual void OnAcceleratedCompositingStateChange() = 0;
   // |params.window| and |params.surface_id| indicate which accelerated