aura-mus: Remove dead code.

ui/views/widget/widget.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 UI_VIEWS_WIDGET_WIDGET_H_
 #define UI_VIEWS_WIDGET_WIDGET_H_
 
 #include <map>
 #include <memory>
 #include <set>
@@ skipping 39 matching lines @@
 
 namespace ui {
 class Accelerator;
 class Compositor;
 class DefaultThemeProvider;
 class InputMethod;
 class Layer;
 class NativeTheme;
 class OSExchangeData;
 class ThemeProvider;
-class Window;
 }  // namespace ui
 
 namespace wm {
 enum class ShadowElevation;
 }
 
 namespace views {
 
 class DesktopWindowTreeHost;
 class NativeWidget;
@@ skipping 176 matching lines @@
     // Specifies that the system default caption and icon should not be
     // rendered, and that the client area should be equivalent to the window
     // area. Only used on some platforms (Windows and Linux).
     bool remove_standard_frame;
     // Only used by ShellWindow on Windows. Specifies that the default icon of
     // packaged app should be the system default icon.
     bool use_system_default_icon;
     // Whether the widget should be maximized or minimized.
     ui::WindowShowState show_state;
     gfx::NativeView parent;
-    // Used only by mus and is necessitated by mus not being a NativeView.
-    ui::Window* parent_mus = nullptr;
     // Specifies the initial bounds of the Widget. Default is empty, which means
     // the NativeWidget may specify a default size. If the parent is specified,
     // |bounds| is in the parent's coordinate system. If the parent is not
     // specified, it's in screen's global coordinate system.
     gfx::Rect bounds;
     // The initial workspace of the Widget.  Default is "", which means the
     // current workspace.
     std::string workspace;
     // When set, this value is used as the Widget's NativeWidget implementation.
     // The Widget will not construct a default one. Default is NULL.
@@ skipping 725 matching lines @@
 
   // Guard to avoid reentrancy while processing a theme changed message.
   bool processing_theme_changed_;
 
   DISALLOW_COPY_AND_ASSIGN(Widget);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_WIDGET_H_