Prepare for -Wall for third-party code, -Wextra for chromium_code

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.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_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 
 #include <stddef.h>
 #include <stdint.h>
 #include <X11/extensions/shape.h>
@@ skipping 78 matching lines @@
   static void CleanUpWindowList(void (*func)(aura::Window* window));
 
   // Disables event listening to make |dialog| modal.
   void DisableEventListening(XID dialog);
 
   // Enables event listening after closing |dialog|.
   void EnableEventListening();
 
   // Returns XID of dialog currently displayed. When it returns 0,
   // there is no dialog on the host window.
-  const XID GetModalDialog();
+  XID GetModalDialog();
 
  protected:
   // Overridden from DesktopWindowTreeHost:
   void Init(aura::Window* content_window,
             const Widget::InitParams& params) override;
   void OnNativeWidgetCreated(const Widget::InitParams& params) override;
   scoped_ptr<corewm::Tooltip> CreateTooltip() override;
   scoped_ptr<aura::client::DragDropClient> CreateDragDropClient(
       DesktopNativeCursorManager* cursor_manager) override;
   void Close() override;
@@ skipping 255 matching lines @@
   XID modal_dialog_xid_;
 
   base::WeakPtrFactory<DesktopWindowTreeHostX11> close_widget_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopWindowTreeHostX11);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_