Revert of Converts chrome to aura-mus

ui/aura/mus/focus_synchronizer.h

Index: ui/aura/mus/focus_synchronizer.h
diff --git a/ui/aura/mus/focus_synchronizer.h b/ui/aura/mus/focus_synchronizer.h
index 8a67a8b02ba192c6132262f8f0c582c365369bc1..db2556d76155f0e1cdb8000f5a0ab6af217f901a 100644
--- a/ui/aura/mus/focus_synchronizer.h
+++ b/ui/aura/mus/focus_synchronizer.h
@@ -17,7 +17,6 @@
 
 namespace aura {
 
-class Env;
 class FocusSynchronizerDelegate;
 class WindowMus;
 
@@ -53,7 +52,6 @@
 
   // Overrided from EnvObserver:
   void OnWindowInitialized(Window* window) override;
-  void OnWillDestroyEnv() override;
   void OnActiveFocusClientChanged(client::FocusClient* focus_client,
                                   Window* window) override;
 
@@ -66,9 +64,6 @@
   WindowMus* window_setting_focus_to_ = nullptr;
   WindowMus* focused_window_ = nullptr;
 
-  // Cached so we can detect if Env is destroyed before us.
-  Env* env_;
-
   DISALLOW_COPY_AND_ASSIGN(FocusSynchronizer);
 };