mash: Migrate ScopedTargetRootWindow to //ash/common

ash/mus/bridge/wm_shell_mus.h

 // Copyright 2016 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_MUS_BRIDGE_WM_SHELL_MUS_H_
 #define ASH_MUS_BRIDGE_WM_SHELL_MUS_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 42 matching lines @@
   AcceleratorControllerDelegateMus* accelerator_controller_delegate() {
     return accelerator_controller_delegate_.get();
   }
 
   // WmShell:
   WmWindow* NewContainerWindow() override;
   WmWindow* GetFocusedWindow() override;
   WmWindow* GetActiveWindow() override;
   WmWindow* GetPrimaryRootWindow() override;
   WmWindow* GetRootWindowForDisplayId(int64_t display_id) override;
-  WmWindow* GetRootWindowForNewWindows() override;
   const DisplayInfo& GetDisplayInfo(int64_t display_id) const override;
   bool IsActiveDisplayId(int64_t display_id) const override;
   bool IsForceMaximizeOnFirstRun() override;
   bool IsPinned() override;
   void SetPinnedWindow(WmWindow* window) override;
   bool CanShowWindowForUser(WmWindow* window) override;
   void LockCursor() override;
   void UnlockCursor() override;
   std::vector<WmWindow*> GetAllRootWindows() override;
   void RecordUserMetricsAction(UserMetricsAction action) override;
@@ skipping 45 matching lines @@
 
   base::ObserverList<WmActivationObserver> activation_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(WmShellMus);
 };
 
 }  // namespace mus
 }  // namespace ash
 
 #endif  // ASH_MUS_BRIDGE_WM_SHELL_MUS_H_