Add user action for changing the active window in Ash overview mode

ash/wm/overview/window_selector_controller.h

Index: ash/wm/overview/window_selector_controller.h
diff --git a/ash/wm/overview/window_selector_controller.h b/ash/wm/overview/window_selector_controller.h
index 8d4a625e13e72ec9aab2c160e03e59900d2648f6..18995d027f3d72248383bd1b682a350ad36e7ec4 100644
--- a/ash/wm/overview/window_selector_controller.h
+++ b/ash/wm/overview/window_selector_controller.h
@@ -54,12 +54,20 @@ class ASH_EXPORT WindowSelectorController
  private:
   friend class WindowSelectorTest;
 
-  // Dispatched when window selection begins.
+  // Called when overview mode is about to be engaged.
+  void OnSelectionStarting();
+
+  // Called when overview mode is engaged.
   void OnSelectionStarted();
 
   scoped_ptr<WindowSelector> window_selector_;
   base::Time last_selection_time_;
 
+  // While overview mode is active, tracks the window of type WINDOW_TYPE_NORMAL
+  // or WINDOW_TYPE_PANEL that was active prior to entering overview mode if
+  // such a window exists (nullptr otherwise).

[oshima, 2015/05/12 20:25:13]

document that the pointer may be stale (if it's closed during overview mode).
you may actually reset the pointer when the window is destroyed, but I'll leave
it to you, as its content isn't accessed.

[tdanderson, 2015/05/14 01:36:32]

I've removed this pointer in patch set 2.

+  aura::Window* initially_active_window_;
+
   DISALLOW_COPY_AND_ASSIGN(WindowSelectorController);
 };