gin: Add ability to install call-as-function handlers on gin::Wrappable

gin/function_template.h.pump

 $$ This is a pump file for generating file templates.  Pump is a python
 $$ script that is part of the Google Test suite of utilities.  Description
 $$ can be found here:
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 #ifndef GIN_FUNCTION_TEMPLATE_H_
 #define GIN_FUNCTION_TEMPLATE_H_
 
@@ skipping 203 matching lines @@
   typedef internal::CallbackHolder<Sig> HolderT;
   HolderT* holder = new HolderT(isolate, callback, callback_flags);
 
   return v8::FunctionTemplate::New(
       isolate,
       &internal::Dispatcher<Sig>::DispatchToCallback,
       ConvertToV8<v8::Handle<v8::External> >(isolate,
                                              holder->GetHandle(isolate)));
 }
 
+// CreateFunctionHandler installs a CallAsFunction handler on the given
+// object template that forwards to a provided C++ function or base::Callback.
+template<typename Sig>
+void CreateFunctionHandler(v8::Isolate* isolate,
+                           v8::Local<v8::ObjectTemplate> tmpl,
+                           const base::Callback<Sig> callback,
+                           int callback_flags = 0) {
+  typedef internal::CallbackHolder<Sig> HolderT;
+  HolderT* holder = new HolderT(isolate, callback, callback_flags);
+  tmpl->SetCallAsFunctionHandler(&internal::Dispatcher<Sig>::DispatchToCallback,
+                                 ConvertToV8<v8::Handle<v8::External> >(
+                                     isolate, holder->GetHandle(isolate)));
+}
+
 }  // namespace gin
 
 #endif  // GIN_FUNCTION_TEMPLATE_H_