chromeos: fix focus for mushrome

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 cca9ebaf2e7a0a78b7ddd445f3f40f5c230e89b7..b2908cb7ce92fd54b188e95840a0025e20ce7136 100644
--- a/ui/aura/mus/focus_synchronizer.h
+++ b/ui/aura/mus/focus_synchronizer.h
@@ -28,7 +28,12 @@ class FocusClient;
 }
 
 // FocusSynchronizer is resonsible for keeping focus in sync between aura
-// and the mus server.
+// and the mus server. FocusSynchronizer may be configured in two distinct
+// ways:
+// . SetSingletonFocusClient(). Use this when a single FocusClient is shared
+//   among all windows and never changes.
+// . SetActiveFocusClient(). Use this when there may be more than one
+//   FocusClient.
 class AURA_EXPORT FocusSynchronizer : public client::FocusChangeObserver,
                                       public WindowObserver {
  public:
@@ -51,6 +56,11 @@ class AURA_EXPORT FocusSynchronizer : public client::FocusChangeObserver,
   // Called when the focused window is destroyed.
   void OnFocusedWindowDestroyed();
 
+  // Used when the focus client is shared among all windows. See class
+  // description for details.
+  void SetSingletonFocusClient(client::FocusClient* focus_client);
+  bool is_singleton_focus_client() const { return is_singleton_focus_client_; }
+
   // Sets the active FocusClient and the window the FocusClient is associated
   // with. |focus_client_root| is not necessarily the window that actually has
   // focus.
@@ -86,6 +96,8 @@ class AURA_EXPORT FocusSynchronizer : public client::FocusChangeObserver,
   bool setting_focus_ = false;
   WindowMus* window_setting_focus_to_ = nullptr;
 
+  bool is_singleton_focus_client_ = false;
+
   client::FocusClient* active_focus_client_ = nullptr;
   // The window that |active_focus_client_| is associated with.
   Window* active_focus_client_root_ = nullptr;