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

ppapi/proxy/printing_resource.h

Index: ppapi/proxy/printing_resource.h
diff --git a/ppapi/proxy/printing_resource.h b/ppapi/proxy/printing_resource.h
index 0ea677544dfd493689bf84502dee50c465df2a5c..deaa1f5cb78dc2a805976d2afadf2c257fd1fb91 100644
--- a/ppapi/proxy/printing_resource.h
+++ b/ppapi/proxy/printing_resource.h
@@ -20,13 +20,13 @@ class PPAPI_PROXY_EXPORT PrintingResource
  public:
   PrintingResource(Connection connection,
                    PP_Instance instance);
-  virtual ~PrintingResource();
+  ~PrintingResource() override;
 
   // Resource overrides.
-  virtual thunk::PPB_Printing_API* AsPPB_Printing_API() override;
+  thunk::PPB_Printing_API* AsPPB_Printing_API() override;
 
   // PPB_Printing_API.
-  virtual int32_t GetDefaultPrintSettings(
+  int32_t GetDefaultPrintSettings(
       PP_PrintSettings_Dev* print_settings,
       scoped_refptr<TrackedCallback> callback) override;