Use v8::Context::kDebugIdIndex instead of hardwired constant in gin

gin/public/context_holder.h

 // Copyright 2013 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_CONTEXT_HOLDER_H_
 #define GIN_PUBLIC_CONTEXT_HOLDER_H_
 
 #include <list>
 
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "gin/gin_export.h"
 #include "v8/include/v8.h"
 
 namespace gin {
 
 // Gin embedder that store embedder data in v8::Contexts must do so in a
 // single field with the index kPerContextDataStartIndex + GinEmbedder-enum.
 // The field at kDebugIdIndex is treated specially by V8 and is reserved for
 // a V8 debugger implementation (not used by gin).
 enum ContextEmbedderDataFields {
-  kDebugIdIndex = 0,
+  kDebugIdIndex = v8::Context::kDebugIdIndex,
   kPerContextDataStartIndex,
 };
 
 class PerContextData;
 
 // ContextHolder is a generic class for holding a v8::Context.
 class GIN_EXPORT ContextHolder {
  public:
   explicit ContextHolder(v8::Isolate* isolate);
   ~ContextHolder();
@@ skipping 10 matching lines @@
   v8::Isolate* isolate_;
   v8::UniquePersistent<v8::Context> context_;
   scoped_ptr<PerContextData> data_;
 
   DISALLOW_COPY_AND_ASSIGN(ContextHolder);
 };
 
 }  // namespace gin
 
 #endif  // GIN_PUBLIC_CONTEXT_HOLDER_H_