Reland: Mojo: add javascript bindings for request/response

mojo/public/bindings/tests/sample_interfaces.mojom

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module sample {
 
-struct Coord {
-  int32 x;
-  int32 y;
-};
-
 [Peer=ProviderClient]
 interface Provider {
   EchoString(string a) => (string a);
   EchoStrings(string a, string b) => (string a, string b);
   EchoMessagePipeHandle(handle<message_pipe> a) => (handle<message_pipe> a);
-  //EchoVoid() => ();
-  //MakeCoord(int32 x, int32 y) => (Coord coord);
-  //Make2Coords(int32 x1, int32 y1, int32 x2, int32 y2) =>
-  //    (Coord coord1, Coord coord2);
 };
 
 [Peer=Provider]
 interface ProviderClient {
 };
 
 }