chromeos: Eliminate WmWindow from //ash/system

ash/system/palette/palette_tray.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_SYSTEM_PALETTE_PALETTE_TRAY_H_
 #define ASH_SYSTEM_PALETTE_PALETTE_TRAY_H_
 
 #include <memory>
 
 #include "ash/ash_export.h"
@@ skipping 75 matching lines @@
   void OnMouseExitedView() override;
   base::string16 GetAccessibleNameForBubble() override;
   void OnBeforeBubbleWidgetInit(
       views::Widget* anchor_widget,
       views::Widget* bubble_widget,
       views::Widget::InitParams* params) const override;
   void HideBubble(const views::TrayBubbleView* bubble_view) override;
 
   // PaletteToolManager::Delegate:
   void OnActiveToolChanged() override;
-  WmWindow* GetWindow() override;
+  aura::Window* GetWindow() override;
 
   // Updates the tray icon from the palette tool manager.
   void UpdateTrayIcon();
 
   // Sets the icon to visible if the palette can be used.
   void UpdateIconVisibility();
 
   // Called when the palette enabled pref has changed.
   void OnPaletteEnabledPrefChanged(bool enabled);
 
@@ skipping 21 matching lines @@
   ScopedSessionObserver scoped_session_observer_;
 
   base::WeakPtrFactory<PaletteTray> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(PaletteTray);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_PALETTE_PALETTE_TRAY_H_