Prevent browser thumbnailer from trying to read from frontbuffer (surface texture) when none exists.

chrome/browser/tab_contents/thumbnail_generator.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 CHROME_BROWSER_TAB_CONTENTS_THUMBNAIL_GENERATOR_H_
 #define CHROME_BROWSER_TAB_CONTENTS_THUMBNAIL_GENERATOR_H_
 #pragma once
 
 #include <map>
 #include <utility>
@@ skipping 123 matching lines @@
                                    ClipResult* clip_result);
 
   // Update the thumbnail of the given tab contents if necessary.
   void UpdateThumbnailIfNecessary(content::WebContents* webb_contents);
 
   // Update the thumbnail of the given tab.
   void UpdateThumbnail(content::WebContents* web_contents,
                        const SkBitmap& bitmap,
                        const ThumbnailGenerator::ClipResult& clip_result);
 
   // Returns true if we should update the thumbnail of the given URL.

[mazda, 2012/05/03 19:57:31]

URL -> web contents

-  static bool ShouldUpdateThumbnail(Profile* profile,
-                                    history::TopSites* top_sites,
-                                    const GURL& url);
+  static bool ShouldUpdateThumbnail(content::WebContents* web_contents);
 
   // content::WebContentsObserver overrides.
   virtual void DidStartLoading() OVERRIDE;
   virtual void StopNavigation() OVERRIDE;
 
  private:
   virtual void WidgetDidReceivePaintAtSizeAck(
       content::RenderWidgetHost* widget,
       int tag,
       const gfx::Size& size);
@@ skipping 33 matching lines @@
   bool load_interrupted_;
 
   base::WeakPtrFactory<ThumbnailGenerator> weak_factory_;
   scoped_ptr<base::WeakPtrFactory<content::WebContents> >
       web_contents_weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ThumbnailGenerator);
 };
 
 #endif  // CHROME_BROWSER_TAB_CONTENTS_THUMBNAIL_GENERATOR_H_