Add the "virtual" keyword on method overrides that are missing it.

webkit/glue/plugins/pepper_file_system.h

 // Copyright (c) 2010 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 WEBKIT_GLUE_PLUGINS_PEPPER_FILE_SYSTEM_H_
 #define WEBKIT_GLUE_PLUGINS_PEPPER_FILE_SYSTEM_H_
 
 #include "base/basictypes.h"
 #include "base/file_path.h"
 #include "ppapi/c/dev/pp_file_info_dev.h"
 #include "webkit/glue/plugins/pepper_resource.h"
 
 struct PPB_FileSystem_Dev;
 
 namespace pepper {
 
 class PluginInstance;
 
 class FileSystem : public Resource {
  public:
   // Returns a pointer to the interface implementing PPB_FileSystem that is
   // exposed to the plugin.
   static const PPB_FileSystem_Dev* GetInterface();
 
   FileSystem(PluginInstance* instance, PP_FileSystemType_Dev type);
-  FileSystem* AsFileSystem() { return this; }
+  virtual FileSystem* AsFileSystem();
 
   PluginInstance* instance() { return instance_; }
   PP_FileSystemType_Dev type() { return type_; }
   const FilePath& root_path() const { return root_path_; }
   void set_root_path(const FilePath& root_path) { root_path_ = root_path; }
   bool opened() const { return opened_; }
   void set_opened(bool opened) { opened_ = opened; }
 
  private:
   PluginInstance* instance_;
   PP_FileSystemType_Dev type_;
   FilePath root_path_;
   bool opened_;
 };
 
 }  // namespace pepper
 
 #endif  // WEBKIT_GLUE_PLUGINS_PEPPER_FILE_SYSTEM_H_