athena: Allow getting into split-view mode from overview-mode.

athena/wm/window_overview_mode.h

 // Copyright 2014 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 ATHENA_WM_WINDOW_OVERVIEW_MODE_H_
 #define ATHENA_WM_WINDOW_OVERVIEW_MODE_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "ui/aura/window.h"
 
 namespace athena {
 class WindowListProvider;
 
 class WindowOverviewModeDelegate {
  public:
   virtual ~WindowOverviewModeDelegate() {}
 
   virtual void OnSelectWindow(aura::Window* window) = 0;
+
+  // Gets into split-view mode with |left| on the left-side of the screen, and
+  // |right| on the right-side. If |left| or |right| is NULL, then the delegate
+  // selects the best option in its place.
+  virtual void OnSplitViewMode(aura::Window* left,
+                               aura::Window* right) = 0;
 };
 
 class WindowOverviewMode {
  public:
   virtual ~WindowOverviewMode() {}
 
   static scoped_ptr<WindowOverviewMode> Create(
       aura::Window* container,
       const WindowListProvider* window_list_provider,
       WindowOverviewModeDelegate* delegate);
 };
 
 }  // namespace athena
 
 #endif  // ATHENA_WM_WINDOW_OVERVIEW_MODE_H_