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

ppapi/proxy/broker_dispatcher.h

Index: ppapi/proxy/broker_dispatcher.h
diff --git a/ppapi/proxy/broker_dispatcher.h b/ppapi/proxy/broker_dispatcher.h
index ea2b4770727f1321e16b479e7c9557ffb0c821d5..828dac63666a67ba4493927d4582950f7c5867d6 100644
--- a/ppapi/proxy/broker_dispatcher.h
+++ b/ppapi/proxy/broker_dispatcher.h
@@ -14,7 +14,7 @@ namespace proxy {
 
 class PPAPI_PROXY_EXPORT BrokerDispatcher : public ProxyChannel {
  public:
-  virtual ~BrokerDispatcher();
+  ~BrokerDispatcher() override;
 
   // You must call this function before anything else. Returns true on success.
   // The delegate pointer must outlive this class, ownership is not
@@ -25,7 +25,7 @@ class PPAPI_PROXY_EXPORT BrokerDispatcher : public ProxyChannel {
                                      bool is_client);
 
   // IPC::Listener implementation.
-  virtual bool OnMessageReceived(const IPC::Message& msg) override;
+  bool OnMessageReceived(const IPC::Message& msg) override;
 
  protected:
   // You must call InitBrokerWithChannel after the constructor.
@@ -47,7 +47,7 @@ class PPAPI_PROXY_EXPORT BrokerHostDispatcher : public BrokerDispatcher {
   BrokerHostDispatcher();
 
   // IPC::Listener implementation.
-  virtual void OnChannelError() override;
+  void OnChannelError() override;
 };
 
 // The dispatcher for the broker side of the broker channel.
@@ -56,7 +56,7 @@ class PPAPI_PROXY_EXPORT BrokerSideDispatcher : public BrokerDispatcher {
   explicit BrokerSideDispatcher(PP_ConnectInstance_Func connect_instance);
 
   // IPC::Listener implementation.
-  virtual void OnChannelError() override;
+  void OnChannelError() override;
 };
 
 }  // namespace proxy