Gin: Consolidate all the Converter<Wrappable> subclasses.

gin/function_template.h

Index: gin/function_template.h
diff --git a/gin/function_template.h b/gin/function_template.h
index b2badfa7dfb48d58f6ab9822aacb97bfbb01488e..67df90e966246e64f0a3d663ba223347c078ef45 100644
--- a/gin/function_template.h
+++ b/gin/function_template.h
@@ -32,6 +32,7 @@ enum CreateFunctionTemplateFlags {
 
 namespace internal {
 
+// TODO(aa): Move this to base/template_util.h as remove_const.
 template<typename T>
 struct CallbackParamTraits {
   typedef T LocalType;
@@ -333,14 +334,6 @@ struct Dispatcher<R(P1, P2, P3, P4)> {
 void InitFunctionTemplates(PerIsolateData* isolate_data);
 
 
-// This has to be outside the internal namespace because template
-// specializations must be declared in the same namespace as the original
-// template.
-template<>
-struct Converter<internal::CallbackHolderBase*>
-    : public WrappableConverter<internal::CallbackHolderBase> {};
-
-
 // CreateFunctionTemplate creates a v8::FunctionTemplate that will create
 // JavaScript functions that execute a provided C++ function or base::Callback.
 // JavaScript arguments are automatically converted via gin::Converter, as is