Mojo: more idiomatic C++ bindings

mojo/public/interfaces/bindings/tests/test_structs.mojom

 // Copyright 2013 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.
 
 [JavaPackage="org.chromium.mojo.bindings.test"]
-module test_structs {
+module mojo.test {
 
 struct Rect {
   int32 x;
   int32 y;
   int32 width;
   int32 height;
 };
 
 struct NamedRegion {
   string name;
   Rect[] rects;
 };
 
+struct RectPair {
+  Rect first;
+  Rect second;
+};
+
 }