Support default values for POD struct fields in mojom IDL.

mojo/public/bindings/sample/sample_service_unittests.js

 // 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.
 
 define([
     "console",
     "mojo/apps/js/test/hexdump",
     "gin/test/expect",
     "mojom/sample_service"
   ], function(console, hexdump, expect, sample) {
@@ skipping 67 matching lines @@
       expect(foo.extra_bars[i].type).toBe(type);
     }
 
     expect(foo.data.length).toBe(10);
     for (var i = 0; i < foo.data.length; ++i)
       expect(foo.data[i]).toBe(foo.data.length - i);
 
     expect(foo.source).toBe(0xFFFF);
   }
 
+  // Check that values are set to the defaults if we don't override them.
+  function checkDefaultValues() {
+    var bar = new sample.Bar();
+    expect(bar.alpha).toBe(255);
+
+    var foo = new sample.Foo();
+    expect(foo.name).toBe("Fooby");
+    expect(foo.a).toBeTruthy();
+  }
+
   function ServiceImpl() {
   }
 
   ServiceImpl.prototype = Object.create(sample.ServiceStub.prototype);
 
   ServiceImpl.prototype.frobinate = function(foo, baz, port) {
     checkFoo(foo);
     expect(baz).toBe(sample.ServiceStub.BazOptions.BAZ_EXTRA);
     expect(port).toBe(10);
     global.result = "PASS";
   };
 
   function SimpleMessageReceiver() {
   }
 
   SimpleMessageReceiver.prototype.accept = function(message) {
     if (dumpMessageAsHex)
       console.log(hexdump.dumpArray(message.memory));
     // Imagine some IPC happened here.
     var serviceImpl = new ServiceImpl();
     serviceImpl.accept(message);
   };
 
   var receiver = new SimpleMessageReceiver();
   var serviceProxy = new sample.ServiceProxy(receiver);
 
+  checkDefaultValues();
+
   var foo = makeFoo();
   checkFoo(foo);
 
   var port = 10;
   serviceProxy.frobinate(foo, sample.ServiceProxy.BazOptions.BAZ_EXTRA, port);
 });