Make URLDataSource::GetSource() const.

chrome/browser/ui/webui/bookmarks_ui.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_BOOKMARKS_UI_H_
 #define CHROME_BROWSER_UI_WEBUI_BOOKMARKS_UI_H_
 
 #include <string>
 
 #include "base/compiler_specific.h"
 #include "content/public/browser/url_data_source.h"
 #include "content/public/browser/web_ui_controller.h"
 #include "ui/base/layout.h"
 
 namespace base {
 class RefCountedMemory;
 }
 
 // This class provides the source for chrome://bookmarks/
 class BookmarksUIHTMLSource : public content::URLDataSource {
  public:
   BookmarksUIHTMLSource();
 
   // 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;
 
  private:
   virtual ~BookmarksUIHTMLSource();
 
   DISALLOW_COPY_AND_ASSIGN(BookmarksUIHTMLSource);
 };
 
 // This class is used to hook up chrome://bookmarks/ which in turn gets
 // overridden by an extension.
 class BookmarksUI : public content::WebUIController {
  public:
   explicit BookmarksUI(content::WebUI* web_ui);
 
   static base::RefCountedMemory* GetFaviconResourceBytes(
       ui::ScaleFactor scale_factor);
 
  private:
   DISALLOW_COPY_AND_ASSIGN(BookmarksUI);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_BOOKMARKS_UI_H_