mus: Allow the WM to specify the windows that can have active children.

components/mus/ws/focus_controller.h

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_MUS_WS_FOCUS_CONTROLLER_H_
 #define COMPONENTS_MUS_WS_FOCUS_CONTROLLER_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "components/mus/ws/server_window_drawn_tracker_observer.h"
 
@@ skipping 24 matching lines @@
   // Describes the source of the change.
   enum ChangeSource {
     CHANGE_SOURCE_EXPLICIT,
     CHANGE_SOURCE_DRAWN_STATE_CHANGED,
   };
 
   // Returns whether |window| can be focused or activated.
   bool CanBeFocused(ServerWindow* window) const;
   bool CanBeActivated(ServerWindow* window) const;
 
+  // Returns the closest activatable ancestor of |window|. Returns nullptr if
+  // there is no such ancestor.
+  ServerWindow* GetActivatableAncestorOf(ServerWindow* window) const;
+
   // Implementation of SetFocusedWindow().
   void SetFocusedWindowImpl(ServerWindow* window, ChangeSource change_source);
 
   // ServerWindowDrawnTrackerObserver:
   void OnDrawnStateChanged(ServerWindow* ancestor,
                            ServerWindow* window,
                            bool is_drawn) override;
 
   FocusControllerDelegate* delegate_;
+
+  ServerWindow* focused_window_;
+  ServerWindow* active_window_;
+
+  // Keeps track of the visibility of the focused and active window.
   scoped_ptr<ServerWindowDrawnTracker> drawn_tracker_;
 
   DISALLOW_COPY_AND_ASSIGN(FocusController);
 };
 
 }  // namespace ws
 
 }  // namespace mus
 
 #endif  // COMPONENTS_MUS_WS_FOCUS_CONTROLLER_H_