Makes PlatformEventSource creation in Env conditional

ui/aura/env.h

Index: ui/aura/env.h
diff --git a/ui/aura/env.h b/ui/aura/env.h
index 1d6c19de3fb07a4a15b1cab5fd84e714daa09438..159ac480d096a7c788b14e9167536d38b82a3260 100644
--- a/ui/aura/env.h
+++ b/ui/aura/env.h
@@ -32,7 +32,11 @@ class AURA_EXPORT Env : public ui::EventTarget {
   Env();
   virtual ~Env();
 
-  static void CreateInstance();
+  // Creates the single Env instance (if it hasn't been created yet). If
+  // |create_event_source| is true a PlatformEventSource is created.
+  // TODO(sky): nuke |create_event_source|. Only necessary while mojo's
+  // nativeviewportservice lives in the same process as the viewmanager.
+  static void CreateInstance(bool create_event_source);
   static Env* GetInstance();
   static void DeleteInstance();
 
@@ -63,7 +67,8 @@ class AURA_EXPORT Env : public ui::EventTarget {
   friend class Window;
   friend class WindowTreeHost;
 
-  void Init();
+  // See description of CreateInstance() for deatils of |create_event_source|.
+  void Init(bool create_event_source);
 
   // Called by the Window when it is initialized. Notifies observers.
   void NotifyWindowInitialized(Window* window);