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 db2556d76155f0e1cdb8000f5a0ab6af217f901a..8a67a8b02ba192c6132262f8f0c582c365369bc1 100644
--- a/ui/aura/mus/focus_synchronizer.h
+++ b/ui/aura/mus/focus_synchronizer.h
@@ -17,6 +17,7 @@ class WindowTree;
 
 namespace aura {
 
+class Env;
 class FocusSynchronizerDelegate;
 class WindowMus;
 
@@ -52,6 +53,7 @@ class FocusSynchronizer : public client::FocusChangeObserver,
 
   // Overrided from EnvObserver:
   void OnWindowInitialized(Window* window) override;
+  void OnWillDestroyEnv() override;
   void OnActiveFocusClientChanged(client::FocusClient* focus_client,
                                   Window* window) override;
 
@@ -64,6 +66,9 @@ class FocusSynchronizer : public client::FocusChangeObserver,
   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);
 };