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

ash/wm/workspace_controller.h

 // Copyright (c) 2012 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_CONTROLLER_H_
 #define ASH_WM_WORKSPACE_CONTROLLER_H_
 #pragma once
 
 #include "ash/launcher/launcher_model_observer.h"
-#include "ash/wm/workspace/workspace_observer.h"
 #include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/aura/root_window_observer.h"
 #include "ui/aura/window_observer.h"
 #include "ash/ash_export.h"
 
 namespace aura {
 class Window;
 }
 
 namespace gfx {
 class Size;
 }
 
 namespace ash {
 class LauncherModel;
 
 namespace internal {
 
 class WorkspaceManager;
 
 // WorkspaceController owns a WorkspaceManager. WorkspaceController bridges
 // events from RootWindowObserver translating them to WorkspaceManager, and
 // a move event between Launcher and Workspace.
 class ASH_EXPORT WorkspaceController :
       public aura::RootWindowObserver,
       public aura::WindowObserver,
-      public ash::internal::WorkspaceObserver,
       public ash::LauncherModelObserver {
  public:
   explicit WorkspaceController(aura::Window* workspace_viewport);
   virtual ~WorkspaceController();
 
   void ToggleOverview();
 
   void SetLauncherModel(LauncherModel* launcher_model);
 
   // Returns the workspace manager that this controler owns.
   WorkspaceManager* workspace_manager() {
     return workspace_manager_.get();
   }
 
   // aura::RootWindowObserver overrides:
   virtual void OnRootWindowResized(const gfx::Size& new_size) OVERRIDE;
 
   // aura::WindowObserver overrides:
   virtual void OnWindowPropertyChanged(aura::Window* window,
                                        const char* key,
                                        void* old) OVERRIDE;
 
-  // WorkspaceObserver overrides:
-  virtual void WindowMoved(WorkspaceManager* manager,
-                           aura::Window* source,
-                           aura::Window* target) OVERRIDE;
-  virtual void ActiveWorkspaceChanged(WorkspaceManager* manager,
-                                      Workspace* old) OVERRIDE;
-
   // Invoked after an item has been added to the model.
   virtual void LauncherItemAdded(int index) OVERRIDE;
   virtual void LauncherItemRemoved(int index) OVERRIDE;
   virtual void LauncherItemMoved(int start_index, int target_index) OVERRIDE;
   virtual void LauncherItemChanged(int index,
                                    const ash::LauncherItem& old_item) OVERRIDE;
   virtual void LauncherItemWillChange(int index) OVERRIDE {}
 
  private:
   scoped_ptr<WorkspaceManager> workspace_manager_;
 
   // Owned by Launcher.
   LauncherModel* launcher_model_;
 
   // True while the controller is moving window either on workspace or launcher.
   // Used to prevent infinite recursive call between the workspace and launcher.
   bool ignore_move_event_;
 
   DISALLOW_COPY_AND_ASSIGN(WorkspaceController);
 };
 
 }  // namespace internal
 }  // namespace ash
 
 #endif  // ASH_WM_WORKSPACE_CONTROLLER_H_