Pass synchronous messages by JSON string.

We are going to use IPC_MESSAGE_HANDLER_DELAY_REPLY to handle
synchronous messages but DictionaryValue is not copyable, so we pass the
JSON string instead.

browser/api/atom_api_event.cc

@@ -39,6 +39,13 @@ v8::Handle<v8::Object> Event::CreateV8Object() {
   return scope.Close(v8_event);
 }
 
+// static
+std::string Event::GetReturnValue(v8::Handle<v8::Object> event) {
+  v8::HandleScope scope;
+  v8::Local<v8::Value> json = event->Get(v8::String::New("returnValue"));
+  return *v8::String::Utf8Value(json);
+}
+
 v8::Handle<v8::Value> Event::New(const v8::Arguments &args) {
   Event* event = new Event;
   event->Wrap(args.This());