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..7e33994eedbacf7b9ee79a22ffb0e7c50c0f7c09 100644
--- a/gin/function_template.h
+++ b/gin/function_template.h
@@ -333,14 +333,6 @@ 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