Reworks the workspace code. Here's the new heuristics:

ash/wm/workspace/workspace_observer.h

-// Copyright (c) 2011 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 ASH_WM_WORKSPACE_WORKSPACE_OBSERVER_H_
-#define ASH_WM_WORKSPACE_WORKSPACE_OBSERVER_H_
-#pragma once
-
-#include "ash/ash_export.h"
-
-namespace aura {
-class Window;
-}
-
-namespace ash {
-namespace internal {
-class Workspace;
-class WorkspaceManager;
-
-// A class to observe changes in workspace state.
-class ASH_EXPORT WorkspaceObserver {
- public:
-  // Invoked when |start| window is moved and inserted
-  // at the |target| window's position by |WorkspaceManager::RotateWindow|.
-  virtual void WindowMoved(WorkspaceManager* manager,
-                           aura::Window* source,
-                           aura::Window* target) = 0;
-
-  // Invoked when the active workspace changes. |old| is
-  // the old active workspace and can be NULL.
-  virtual void ActiveWorkspaceChanged(WorkspaceManager* manager,
-                                      Workspace* old) = 0;
- protected:
-  virtual ~WorkspaceObserver() {}
-};
-
-}  // namespace internal
-}  // namespace ash
-
-#endif  // ASH_WM_WORKSPACE_WORKSPACE_OBSERVER_H_