Add a dependency from Gin to base

gin/context_holder.h

Index: gin/context_holder.h
diff --git a/gin/context_holder.h b/gin/context_holder.h
index c9068d1810fcef4348346b59ddb5500e592387de..b11e1d17c26361346c2d45504270eac82afeaf3a 100644
--- a/gin/context_holder.h
+++ b/gin/context_holder.h
@@ -7,10 +7,13 @@
 
 #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);
@@ -27,6 +30,7 @@ class ContextHolder {
  private:
   v8::Isolate* isolate_;
   v8::Persistent<v8::Context> context_;
+  scoped_ptr<PerContextData> data_;
 
   DISALLOW_COPY_AND_ASSIGN(ContextHolder);
 };