mac: Don't set background color from a frame until frame is displayed

content/browser/renderer_host/render_widget_host_view_mac.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_MAC_H_
 #define CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_MAC_H_
 
 #import <Cocoa/Cocoa.h>
 #include <IOSurface/IOSurface.h>
 #include <stddef.h>
@@ skipping 538 matching lines @@
 
   // Whether a request for begin frames has been issued.
   bool needs_begin_frames_;
 
   // Whether a request to flush input has been issued.
   bool needs_flush_input_;
 
   // The background color of the web content. This color will be drawn when the
   // web content is not able to draw in time.
   SkColor background_color_ = SK_ColorTRANSPARENT;
+  SkColor last_frame_root_background_color_ = SK_ColorTRANSPARENT;
 
   // Factory used to safely scope delayed calls to ShutdownHost().
   base::WeakPtrFactory<RenderWidgetHostViewMac> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderWidgetHostViewMac);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_VIEW_MAC_H_