Make URLDataSource::GetSource() const.

chrome/browser/search/local_ntp_source.h

 // Copyright 2013 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_SEARCH_LOCAL_NTP_SOURCE_H_
 #define CHROME_BROWSER_SEARCH_LOCAL_NTP_SOURCE_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "content/public/browser/url_data_source.h"
 
 // Serves HTML and resources for the local new tab page i.e.
 // chrome-search://local-ntp/local-ntp.html
 class LocalNtpSource : public content::URLDataSource {
  public:
   LocalNtpSource();
 
  private:
   virtual ~LocalNtpSource();
 
   // Overridden from content::URLDataSource:
-  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 bool ShouldServiceRequest(
       const net::URLRequest* request) const OVERRIDE;
 
   DISALLOW_COPY_AND_ASSIGN(LocalNtpSource);
 };
 
 #endif  // CHROME_BROWSER_SEARCH_LOCAL_NTP_SOURCE_H_