Modify ThumbnailStore to make one call to the HistoryBackend using QueryTopUR...

chrome/browser/dom_ui/dom_ui_thumbnail_source.h

 // Copyright (c) 2009 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_DOM_UI_DOM_UI_THUMBNAIL_SOURCE_H_
 #define CHROME_BROWSER_DOM_UI_DOM_UI_THUMBNAIL_SOURCE_H_
 
 #include <set>
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/scoped_ptr.h"
 #include "chrome/browser/dom_ui/chrome_url_data_manager.h"
 #include "chrome/browser/history/history.h"
 
 class Profile;
 class ThumbnailStore;
 
 // ThumbnailSource is the gateway between network-level chrome:
 // requests for thumbnails and the history backend that serves these.
 class DOMUIThumbnailSource : public ChromeURLDataManager::DataSource {
  public:
   explicit DOMUIThumbnailSource(Profile* profile);
-  virtual ~DOMUIThumbnailSource();
 
   // Called when the network layer has requested a resource underneath
   // the path we registered.
   virtual void StartDataRequest(const std::string& path, int request_id);
 
-  // Used only when chromium is invoked with the --thumbnail-store switch.
-  // If StartDataRequest does not return thumbnail data synchronously, this
-  // method will be invoked when the thumbnail data becomes available.
-  virtual void ReturnData(int request_id, scoped_refptr<RefCountedBytes> data);
-
   virtual std::string GetMimeType(const std::string&) const {
     // We need to explicitly return a mime type, otherwise if the user tries to
     // drag the image they get no extension.
     return "image/png";
   }
 
   // Called when thumbnail data is available from the history backend.
   void OnThumbnailDataAvailable(HistoryService::Handle request_handle,
                                 scoped_refptr<RefCountedBytes> data);
 
  private:
   Profile* profile_;
   CancelableRequestConsumerT<int, 0> cancelable_consumer_;
 
-  // A set of outstanding request_id's. These are canceled on destruction.
-  std::set<int> pending_requests_;
-
   // The ThumbnailStore from which thumbnails are requested.
   scoped_refptr<ThumbnailStore> store_;
 
   // Raw PNG representation of the thumbnail to show when the thumbnail
   // database doesn't have a thumbnail for a webpage.
   scoped_refptr<RefCountedBytes> default_thumbnail_;
 
   DISALLOW_COPY_AND_ASSIGN(DOMUIThumbnailSource);
 };
 
 #endif  // CHROME_BROWSER_DOM_UI_DOM_UI_THUMBNAIL_SOURCE_H_