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

ppapi/proxy/ppb_x509_certificate_private_proxy.h

Index: ppapi/proxy/ppb_x509_certificate_private_proxy.h
diff --git a/ppapi/proxy/ppb_x509_certificate_private_proxy.h b/ppapi/proxy/ppb_x509_certificate_private_proxy.h
index b9ad5dfdf3da2ce45c380983b0e003da410e45db..95d8f2cdc64a2dd46bfa15b636b569e715fe20b2 100644
--- a/ppapi/proxy/ppb_x509_certificate_private_proxy.h
+++ b/ppapi/proxy/ppb_x509_certificate_private_proxy.h
@@ -18,11 +18,11 @@ class PPB_X509Certificate_Private_Proxy
     : public InterfaceProxy {
  public:
   explicit PPB_X509Certificate_Private_Proxy(Dispatcher* dispatcher);
-  virtual ~PPB_X509Certificate_Private_Proxy();
+  ~PPB_X509Certificate_Private_Proxy() override;
   static PP_Resource CreateProxyResource(PP_Instance instance);
 
   // InterfaceProxy implementation.
-  virtual bool OnMessageReceived(const IPC::Message& msg) override;
+  bool OnMessageReceived(const IPC::Message& msg) override;
 
   static const ApiID kApiID = API_ID_PPB_X509_CERTIFICATE_PRIVATE;