chromeos: Rename ash::WmShelf to Shelf

ash/system/virtual_keyboard/virtual_keyboard_tray.h

Index: ash/system/virtual_keyboard/virtual_keyboard_tray.h
diff --git a/ash/system/virtual_keyboard/virtual_keyboard_tray.h b/ash/system/virtual_keyboard/virtual_keyboard_tray.h
index 92c43775e02c703347cbdbac4fbc8c39e2a3fc13..c741a03945935223d5f16e05f76be41935dc8c3a 100644
--- a/ash/system/virtual_keyboard/virtual_keyboard_tray.h
+++ b/ash/system/virtual_keyboard/virtual_keyboard_tray.h
@@ -21,7 +21,7 @@ class VirtualKeyboardTray : public TrayBackgroundView,
                             public KeyboardUIObserver,
                             public keyboard::KeyboardControllerObserver {
  public:
-  explicit VirtualKeyboardTray(WmShelf* wm_shelf);
+  explicit VirtualKeyboardTray(Shelf* shelf);
   ~VirtualKeyboardTray() override;
 
   // TrayBackgroundView:
@@ -44,7 +44,7 @@ class VirtualKeyboardTray : public TrayBackgroundView,
   // Weak pointer, will be parented by TrayContainer for its lifetime.
   views::ImageView* icon_;
 
-  WmShelf* wm_shelf_;
+  Shelf* shelf_;
 
   DISALLOW_COPY_AND_ASSIGN(VirtualKeyboardTray);
 };