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 e8cdb243ff2efa5b172238b2ece239b1a9bcf2d4..2ff423ec8486b14f8488e66400f52d3ea8ffe80f 100644
--- a/ui/aura/env.h
+++ b/ui/aura/env.h
@@ -5,6 +5,8 @@
 #ifndef UI_AURA_ENV_H_
 #define UI_AURA_ENV_H_
 
+#include <memory>
+
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/observer_list.h"
@@ -32,14 +34,11 @@ class WindowTreeHost;
 // A singleton object that tracks general state within Aura.
 class AURA_EXPORT Env : public ui::EventTarget, public base::SupportsUserData {
  public:
-  // 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);
+  ~Env() override;
+
+  static std::unique_ptr<Env> CreateInstance();
   static Env* GetInstance();
   static Env* GetInstanceDontCreate();
-  static void DeleteInstance();
 
   void AddObserver(EnvObserver* observer);
   void RemoveObserver(EnvObserver* observer);
@@ -74,10 +73,8 @@ class AURA_EXPORT Env : public ui::EventTarget, public base::SupportsUserData {
   friend class WindowTreeHost;
 
   Env();
-  ~Env() override;
 
-  // See description of CreateInstance() for deatils of |create_event_source|.
-  void Init(bool create_event_source);
+  void Init();
 
   // Called by the Window when it is initialized. Notifies observers.
   void NotifyWindowInitialized(Window* window);