Delete background tab IOSurfaces on Mac.

content/browser/renderer_host/render_widget_host_view_mac.h

Index: content/browser/renderer_host/render_widget_host_view_mac.h
diff --git a/content/browser/renderer_host/render_widget_host_view_mac.h b/content/browser/renderer_host/render_widget_host_view_mac.h
index de4f6f4c0e3d1770742b66b9adfacd3e142925a3..a859d954ffe95da4adeb782efceb39ceae8384b4 100644
--- a/content/browser/renderer_host/render_widget_host_view_mac.h
+++ b/content/browser/renderer_host/render_widget_host_view_mac.h
@@ -285,6 +285,8 @@ class RenderWidgetHostViewMac : public content::RenderWidgetHostViewBase {
       const GpuHostMsg_AcceleratedSurfacePostSubBuffer_Params& params,
       int gpu_host_id) OVERRIDE;
   virtual void AcceleratedSurfaceSuspend() OVERRIDE;
+  virtual bool HasAcceleratedSurface(const gfx::Size& desired_size) OVERRIDE;
+  virtual void AboutToWaitForUpdateMsg() OVERRIDE;
   virtual void GetScreenInfo(WebKit::WebScreenInfo* results) OVERRIDE;
   virtual gfx::Rect GetRootWindowBounds() OVERRIDE;
   virtual gfx::GLSurfaceHandle GetCompositingSurface() OVERRIDE;
@@ -420,8 +422,6 @@ class RenderWidgetHostViewMac : public content::RenderWidgetHostViewBase {
   // selected text on the renderer.
   std::string selected_text_;
 
-  gfx::PluginWindowHandle compositing_surface_;
-
   // List of pending swaps for deferred acking:
   //   pairs of (route_id, gpu_host_id).
   std::list<std::pair<int32, int32> > pending_swap_buffers_acks_;