Make URLDataSource::GetSource() const.

chrome/browser/ui/webui/fileicon_source.cc

 // 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.
 
 #include "chrome/browser/ui/webui/fileicon_source.h"
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/files/file_path.h"
@@ skipping 112 matching lines @@
 
     // Icon was not in cache, go fetch it slowly.
     im->LoadIcon(path,
                  icon_size,
                  base::Bind(&FileIconSource::OnFileIconDataAvailable,
                             base::Unretained(this), details),
                  &cancelable_task_tracker_);
   }
 }
 
-std::string FileIconSource::GetSource() {
+std::string FileIconSource::GetSource() const {
   return kFileIconPath;
 }
 
 void FileIconSource::StartDataRequest(
     const std::string& url_path,
     bool is_incognito,
     const content::URLDataSource::GotDataCallback& callback) {
   std::string query;
   base::FilePath file_path;
   ui::ScaleFactor scale_factor;
@@ skipping 17 matching lines @@
             .sk_bitmap(),
         false,
         &icon_data->data());
 
     details.callback.Run(icon_data);
   } else {
     // TODO(glen): send a dummy icon.
     details.callback.Run(NULL);
   }
 }