Add a dependency from Gin to base

gin/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_CONTEXT_HOLDER_H_
 #define GIN_CONTEXT_HOLDER_H_
 
 #include <list>
 #include "base/basictypes.h"
+#include "base/memory/scoped_ptr.h"
 #include "v8/include/v8.h"
 
 namespace gin {
 
+class PerContextData;
+
 class ContextHolder {
  public:
   explicit ContextHolder(v8::Isolate* isolate);
   ~ContextHolder();
 
   v8::Isolate* isolate() const { return isolate_; }
 
   v8::Handle<v8::Context> context() const {
     return v8::Local<v8::Context>::New(isolate_, context_);
   }
 
   void SetContext(v8::Handle<v8::Context> context);
 
  private:
   v8::Isolate* isolate_;
   v8::Persistent<v8::Context> context_;
+  scoped_ptr<PerContextData> data_;
 
   DISALLOW_COPY_AND_ASSIGN(ContextHolder);
 };
 
 }  // namespace gin
 
 #endif  // GIN_CONTEXT_HOLDER_H_