Revert of aura: Require explicit ownership of the Env instance.

ui/aura/env.h

Index: ui/aura/env.h
diff --git a/ui/aura/env.h b/ui/aura/env.h
index 03c48d2ec70efa8f0c8fa724625514d01025b26e..6fbcb178179a02ee8fbaef2a62ce7238d97e2984 100644
--- a/ui/aura/env.h
+++ b/ui/aura/env.h
@@ -31,11 +31,14 @@
 // A singleton object that tracks general state within Aura.
 class AURA_EXPORT Env : public ui::EventTarget, public base::SupportsUserData {
  public:
-  ~Env() override;
-
-  static scoped_ptr<Env> 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 Env* GetInstanceDontCreate();
+  static void DeleteInstance();
 
   void AddObserver(EnvObserver* observer);
   void RemoveObserver(EnvObserver* observer);
@@ -70,8 +73,10 @@
   friend class WindowTreeHost;
 
   Env();
+  ~Env() override;
 
-  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);