athena: Fix overview mode for split-view mode.

athena/wm/window_overview_mode.h

Index: athena/wm/window_overview_mode.h
diff --git a/athena/wm/window_overview_mode.h b/athena/wm/window_overview_mode.h
index 157b525aa6e2704fa6117012359f8b7525d07aed..b7acf79fa8d8c2a199fcf746bb79929174542687 100644
--- a/athena/wm/window_overview_mode.h
+++ b/athena/wm/window_overview_mode.h
@@ -15,6 +15,12 @@ class WindowOverviewModeDelegate {
  public:
   virtual ~WindowOverviewModeDelegate() {}
 
+  // Returns whether split-view is currently active or not. Sets |left_window|
+  // and |right_window| (if not NULL) if |true| is returned, otherwise both
+  // remain unchanged.
+  virtual bool IsInSplitViewMode(aura::Window** left_window,
+                                 aura::Window** right_window) = 0;
+
   virtual void OnSelectWindow(aura::Window* window) = 0;
 
   // Gets into split-view mode with |left| on the left-side of the screen, and