Makes PlatformEventSource creation in Env conditional

mojo/examples/aura_demo/aura_demo.cc

 // 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.
 
 #include <stdio.h>
 #include <string>
 
 #include "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/message_loop/message_loop.h"
@@ skipping 169 matching lines @@
 extern "C" AURA_DEMO_EXPORT MojoResult CDECL MojoMain(
     MojoHandle shell_handle) {
   CommandLine::Init(0, NULL);
   base::AtExitManager at_exit;
   base::MessageLoop loop;
   mojo::GLES2Initializer gles2;
 
   // TODO(beng): This crashes in a DCHECK on X11 because this thread's
   //             MessageLoop is not of TYPE_UI. I think we need a way to build
   //             Aura that doesn't define platform-specific stuff.
-  aura::Env::CreateInstance();
+  aura::Env::CreateInstance(true);
   mojo::examples::AuraDemo app(shell_handle);
   loop.Run();
 
   return MOJO_RESULT_OK;
 }