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

gin/function_template.h

Index: gin/function_template.h
diff --git a/gin/function_template.h b/gin/function_template.h
index fe95f519ef8a5ddb8e943f6148d2e16068b55d78..7ba54b5910ef4ffcb032deba86a8490a0fba72ef 100644
--- a/gin/function_template.h
+++ b/gin/function_template.h
@@ -501,6 +501,20 @@ v8::Local<v8::FunctionTemplate> CreateFunctionTemplate(
                                              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_