Makes PlatformEventSource creation in Env conditional

ash/shell.cc

 // Copyright (c) 2012 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 "ash/shell.h"
 
 #include <algorithm>
 #include <string>
 
 #include "ash/accelerators/accelerator_controller.h"
@@ skipping 810 matching lines @@
   if (!display_initialized)
     display_manager_->InitDefaultDisplay();
 
   // Install the custom factory first so that views::FocusManagers for Tray,
   // Shelf, and WallPaper could be created by the factory.
   views::FocusManagerFactory::Install(new AshFocusManagerFactory);
 
   // Env creates the compositor. Historically it seems to have been implicitly
   // initialized first by the ActivationController, but now that FocusController
   // no longer does this we need to do it explicitly.
-  aura::Env::CreateInstance();
+  aura::Env::CreateInstance(true);
 
   // The WindowModalityController needs to be at the front of the input event
   // pretarget handler list to ensure that it processes input events when modal
   // windows are active.
   window_modality_controller_.reset(
       new ::wm::WindowModalityController(this));
 
   AddPreTargetHandler(this);
 
   env_filter_.reset(new ::wm::CompoundEventFilter);
@@ skipping 274 matching lines @@
 ////////////////////////////////////////////////////////////////////////////////
 // Shell, aura::client::ActivationChangeObserver implementation:
 
 void Shell::OnWindowActivated(aura::Window* gained_active,
                               aura::Window* lost_active) {
   if (gained_active)
     target_root_window_ = gained_active->GetRootWindow();
 }
 
 }  // namespace ash