[gin] Plumb TraceLogStateObserver into v8.

gin/public/v8_platform.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 GIN_PUBLIC_V8_PLATFORM_H_
 #define GIN_PUBLIC_V8_PLATFORM_H_
 
 #include "base/compiler_specific.h"
 #include "base/lazy_instance.h"
 #include "base/macros.h"
@@ skipping 31 matching lines @@
                          uint64_t bind_id,
                          int32_t num_args,
                          const char** arg_names,
                          const uint8_t* arg_types,
                          const uint64_t* arg_values,
                          unsigned int flags) override;
   void UpdateTraceEventDuration(const uint8_t* category_enabled_flag,
                                 const char* name,
                                 uint64_t handle) override;
 
+  void AddTraceStateObserver(v8::Platform::TraceStateObserver*) override;
+  void RemoveTraceStateObserver(v8::Platform::TraceStateObserver*) override;
+
  private:
   friend struct base::DefaultLazyInstanceTraits<V8Platform>;
 
   V8Platform();
   ~V8Platform() override;
 
   DISALLOW_COPY_AND_ASSIGN(V8Platform);
 };
 
 }  // namespace gin
 
 #endif  // GIN_PUBLIC_V8_PLATFORM_H_