Enforce marking "override" for functions overriding Blink.

content/child/blink_platform_impl.h

 // Copyright 2014 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 CONTENT_CHILD_BLINK_PLATFORM_IMPL_H_
 #define CONTENT_CHILD_BLINK_PLATFORM_IMPL_H_
 
 #include "base/compiler_specific.h"
 #include "base/containers/scoped_ptr_hash_map.h"
 #include "base/threading/thread_local_storage.h"
@@ skipping 101 matching lines @@
                              int max,
                              int bucket_count) override;
   void histogramEnumeration(const char* name,
                             int sample,
                             int boundary_value) override;
   void histogramSparse(const char* name, int sample) override;
   const unsigned char* getTraceCategoryEnabledFlag(
       const char* category_name) override;
   TraceEventAPIAtomicWord* getTraceSamplingState(
       const unsigned thread_bucket) override;
-  virtual TraceEventHandle addTraceEvent(
+  TraceEventHandle addTraceEvent(
       char phase,
       const unsigned char* category_group_enabled,
       const char* name,
       unsigned long long id,
       unsigned long long bind_id,
       double timestamp,
       int num_args,
       const char** arg_names,
       const unsigned char* arg_types,
       const unsigned long long* arg_values,
       blink::WebConvertableToTraceFormat* convertable_values,
-      unsigned int flags);
+      unsigned int flags) override;
   virtual TraceEventHandle addTraceEvent(
       char phase,
       const unsigned char* category_group_enabled,
       const char* name,
       unsigned long long id,
       double timestamp,
       int num_args,
       const char** arg_names,
       const unsigned char* arg_types,
       const unsigned long long* arg_values,
@@ skipping 88 matching lines @@
   scoped_refptr<PushDispatcher> push_dispatcher_;
   scoped_ptr<PermissionDispatcher> permission_client_;
   scoped_ptr<BackgroundSyncProvider> main_thread_sync_provider_;
 
   scheduler::WebThreadBase* compositor_thread_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_CHILD_BLINK_PLATFORM_IMPL_H_