Make URLDataSource::GetSource() const.

chrome/browser/ui/webui/session_favicon_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_SESSION_FAVICON_SOURCE_H_
 #define CHROME_BROWSER_UI_WEBUI_SESSION_FAVICON_SOURCE_H_
 
 #include "chrome/browser/ui/webui/favicon_source.h"
 
 class Profile;
 
 namespace browser_sync {
 class SessionModelAssociator;
 }
 
 // Provides a way to fetch a favicon for a synced tab via a network request.
 class SessionFaviconSource : public FaviconSource {
  public:
   explicit SessionFaviconSource(Profile* profile);
 
   // FaviconSource implementation.
-  virtual std::string GetSource() OVERRIDE;
+  virtual std::string GetSource() const OVERRIDE;
   virtual std::string GetMimeType(const std::string&) const OVERRIDE;
   virtual bool ShouldReplaceExistingSource() const OVERRIDE;
   virtual bool AllowCaching() const OVERRIDE;
 
  protected:
   virtual ~SessionFaviconSource();
   virtual bool HandleMissingResource(const IconRequest& request) OVERRIDE;
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SESSION_FAVICON_SOURCE_H_