Mojo: Use new message APIs to reduce copying

mojo/public/cpp/bindings/lib/interface_endpoint_client.cc

Index: mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
diff --git a/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc b/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
index d7a701b0562b182adcb461eec57197e8f7b07cd0..9e32c5af239b3ff45f5d22a64d0a70165f20d5b1 100644
--- a/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
+++ b/mojo/public/cpp/bindings/lib/interface_endpoint_client.cc
@@ -219,10 +219,11 @@ bool InterfaceEndpointClient::AcceptWithResponder(Message* message,
 
   message->set_request_id(request_id);
 
+  bool is_sync = message->has_flag(kMessageIsSync);
   if (!controller_->SendMessage(message))
     return false;
 
-  if (!message->has_flag(kMessageIsSync)) {
+  if (!is_sync) {
     // We assume ownership of |responder|.
     async_responders_[request_id] = base::WrapUnique(responder);
     return true;