mash: Migrate ScopedTargetRootWindow to //ash/common

ash/common/accelerators/exit_warning_handler.cc

 // Copyright 2013 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.
 
 #include "ash/common/accelerators/exit_warning_handler.h"
 
 #include "ash/common/shell_delegate.h"
 #include "ash/common/shell_window_ids.h"
 #include "ash/common/wm_root_window_controller.h"
 #include "ash/common/wm_shell.h"
@@ skipping 128 matching lines @@
                &ExitWarningHandler::TimerAction);
 }
 
 void ExitWarningHandler::CancelTimer() {
   timer_.Stop();
 }
 
 void ExitWarningHandler::Show() {
   if (widget_)
     return;
-  WmWindow* root_window = WmShell::Get()->GetRootWindowForNewWindows();
+  WmWindow* root_window = WmShell::Get()->root_window_for_new_windows();
   ExitWarningWidgetDelegateView* delegate = new ExitWarningWidgetDelegateView;
   gfx::Size rs = root_window->GetBounds().size();
   gfx::Size ps = delegate->GetPreferredSize();
   gfx::Rect bounds((rs.width() - ps.width()) / 2,
                    (rs.height() - ps.height()) / 3, ps.width(), ps.height());
   views::Widget::InitParams params;
   params.type = views::Widget::InitParams::TYPE_POPUP;
   params.opacity = views::Widget::InitParams::TRANSLUCENT_WINDOW;
   params.ownership = views::Widget::InitParams::WIDGET_OWNS_NATIVE_WIDGET;
   params.accept_events = false;
@@ skipping 10 matching lines @@
   widget_->Show();
 
   delegate->NotifyAccessibilityEvent(ui::AX_EVENT_ALERT, true);
 }
 
 void ExitWarningHandler::Hide() {
   widget_.reset();
 }
 
 }  // namespace ash