Use override keyword in ppapi::proxy::InterfaceProxy.

Instead of virtual, since it inherits from IPC::Sender.
Do the same for child classes and fix lint errors.

Change-Id: Ie01bdd94d0606ce5d2f9e38e08707224c477ac91
Reviewed-on: https://chromium-review.googlesource.com/642461
Commit-Queue: Lei Zhang <[email protected]>
Reviewed-by: Bill Budge <[email protected]>
Cr-Commit-Position: refs/heads/master@{#498678}
diff --git a/ppapi/proxy/ppp_instance_proxy.h b/ppapi/proxy/ppp_instance_proxy.h
index 7eda2bd..c8a4b464 100644
--- a/ppapi/proxy/ppp_instance_proxy.h
+++ b/ppapi/proxy/ppp_instance_proxy.h
@@ -26,7 +26,7 @@
 class PPP_Instance_Proxy : public InterfaceProxy {
  public:
   explicit PPP_Instance_Proxy(Dispatcher* dispatcher);
-  virtual ~PPP_Instance_Proxy();
+  ~PPP_Instance_Proxy() override;
 
   static const PPP_Instance* GetInstanceInterface();
 
@@ -35,7 +35,7 @@
   }
 
   // InterfaceProxy implementation.
-  virtual bool OnMessageReceived(const IPC::Message& msg);
+  bool OnMessageReceived(const IPC::Message& msg) override;
 
  private:
   // Message handlers.