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 "base/observer_list.h"
 #include "components/mus/ws/server_window_drawn_tracker_observer.h"
 
 namespace mus {
 
 namespace ws {
 
+class FocusControllerDelegate;
 class FocusControllerObserver;
 class ServerWindow;
 class ServerWindowDrawnTracker;
 
 // Describes the source of the change.
 enum class FocusControllerChangeSource {
   EXPLICIT,
   DRAWN_STATE_CHANGED,
 };
 
 // Tracks the focused window. Focus is moved to another window when the drawn
 // state of the focused window changes.
 class FocusController : public ServerWindowDrawnTrackerObserver {
  public:
-  FocusController();
+  explicit FocusController(FocusControllerDelegate* delegate);
   ~FocusController() override;
 
   // Sets the focused window. Does nothing if |window| is currently focused.
   // This does not notify the delegate.
   void SetFocusedWindow(ServerWindow* window);
   ServerWindow* GetFocusedWindow();
 
-  // Moves activation to the next activatable window.
-  void CycleActivationForward();
-
   void AddObserver(FocusControllerObserver* observer);
   void RemoveObserver(FocusControllerObserver* observer);
 
  private:
   // 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(FocusControllerChangeSource change_source,
                             ServerWindow* window);
 
   // ServerWindowDrawnTrackerObserver:
   void OnDrawnStateChanged(ServerWindow* ancestor,
                            ServerWindow* window,
                            bool is_drawn) override;
 
+  FocusControllerDelegate* delegate_;
+
+  ServerWindow* focused_window_;
+  ServerWindow* active_window_;
+
   base::ObserverList<FocusControllerObserver> observers_;
+
+  // 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_