Update {virtual,override} to follow C++11 style in ppapi.

ppapi/proxy/dispatcher.h

Index: ppapi/proxy/dispatcher.h
diff --git a/ppapi/proxy/dispatcher.h b/ppapi/proxy/dispatcher.h
index 38ec51ceb006b4eba61d67c6daa552f88efb895d..302884150e438eb39710a43aa42c0d180c316ff1 100644
--- a/ppapi/proxy/dispatcher.h
+++ b/ppapi/proxy/dispatcher.h
@@ -48,7 +48,7 @@ class VarSerializationRules;
 //                                      |
 class PPAPI_PROXY_EXPORT Dispatcher : public ProxyChannel {
  public:
-  virtual ~Dispatcher();
+  ~Dispatcher() override;
 
   // Returns true if the dispatcher is on the plugin side, or false if it's the
   // browser side.
@@ -67,7 +67,7 @@ class PPAPI_PROXY_EXPORT Dispatcher : public ProxyChannel {
   void AddIOThreadMessageFilter(scoped_refptr<IPC::MessageFilter> filter);
 
   // IPC::Listener implementation.
-  virtual bool OnMessageReceived(const IPC::Message& msg) override;
+  bool OnMessageReceived(const IPC::Message& msg) override;
 
   PP_GetInterface_Func local_get_interface() const {
     return local_get_interface_;