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

ppapi/shared_impl/ppb_instance_shared.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PPAPI_SHARED_IMPL_PPB_INSTANCE_SHARED_H_
 #define PPAPI_SHARED_IMPL_PPB_INSTANCE_SHARED_H_
 
 #include "base/compiler_specific.h"
 #include "ppapi/c/pp_stdint.h"
 #include "ppapi/shared_impl/ppapi_shared_export.h"
 #include "ppapi/thunk/ppb_instance_api.h"
 
 namespace ppapi {
 
 class PPAPI_SHARED_EXPORT PPB_Instance_Shared
     : NON_EXPORTED_BASE(public thunk::PPB_Instance_API) {
  public:
-  virtual ~PPB_Instance_Shared();
+  ~PPB_Instance_Shared() override;
 
   // Implementation of some shared PPB_Instance_FunctionAPI functions.
-  virtual void Log(PP_Instance instance,
-                   PP_LogLevel log_level,
-                   PP_Var value) override;
-  virtual void LogWithSource(PP_Instance instance,
-                             PP_LogLevel log_level,
-                             PP_Var source,
-                             PP_Var value) override;
+  void Log(PP_Instance instance, PP_LogLevel log_level, PP_Var value) override;
+  void LogWithSource(PP_Instance instance,
+                     PP_LogLevel log_level,
+                     PP_Var source,
+                     PP_Var value) override;
 
   // Error checks the given resquest to Request[Filtering]InputEvents. Returns
   // PP_OK if the given classes are all valid, PP_ERROR_NOTSUPPORTED if not.
   int32_t ValidateRequestInputEvents(bool is_filtering, uint32_t event_classes);
 
   bool ValidateSetCursorParams(PP_MouseCursor_Type type,
                                PP_Resource image,
                                const PP_Point* hot_spot);
 
   // The length of text to request as a surrounding context of selection.
   // For now, the value is copied from the one with render_view_impl.cc.
   // TODO(kinaba) implement a way to dynamically sync the requirement.
   static const int kExtraCharsForTextInput;
 };
 
 }  // namespace ppapi
 
 #endif  // PPAPI_SHARED_IMPL_PPB_INSTANCE_SHARED_H_