Make URLDataSource::GetSource() const.

chrome/browser/ui/webui/ntp/thumbnail_source.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_UI_WEBUI_NTP_THUMBNAIL_SOURCE_H_
 #define CHROME_BROWSER_UI_WEBUI_NTP_THUMBNAIL_SOURCE_H_
 
 #include <map>
 #include <string>
 
@@ skipping 11 matching lines @@
 class ThumbnailService;
 }
 
 // ThumbnailSource is the gateway between network-level chrome: requests for
 // thumbnails and the history/top-sites backend that serves these.
 class ThumbnailSource : public content::URLDataSource {
  public:
   explicit ThumbnailSource(Profile* profile);
 
   // content::URLDataSource implementation.
-  virtual std::string GetSource() OVERRIDE;
+  virtual std::string GetSource() const OVERRIDE;
   virtual void StartDataRequest(
       const std::string& path,
       bool is_incognito,
       const content::URLDataSource::GotDataCallback& callback) OVERRIDE;
   virtual std::string GetMimeType(const std::string& path) const OVERRIDE;
   virtual base::MessageLoop* MessageLoopForRequestPath(
       const std::string& path) const OVERRIDE;
   virtual bool ShouldServiceRequest(
       const net::URLRequest* request) const OVERRIDE;
 
@@ skipping 15 matching lines @@
   // to the StartDataRequest() call.
   mutable std::map<std::string, std::string> id_to_url_map_;
 
   // Only used when servicing requests on the UI thread.
   Profile* const profile_;
 
   DISALLOW_COPY_AND_ASSIGN(ThumbnailSource);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_NTP_THUMBNAIL_SOURCE_H_