Remove DisplayChangeObserver ash dependencies.

ash/display/shutdown_observer_chromeos.cc

+// 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.
+
+#include "ash/display/shutdown_observer_chromeos.h"
+
+#include "ash/common/wm_shell.h"
+#include "ui/display/manager/chromeos/display_configurator.h"
+
+namespace ash {
+
+ShutdownObserver::ShutdownObserver(
+    ui::DisplayConfigurator* display_configurator)
+    : display_configurator_(display_configurator) {
+  WmShell::Get()->AddShellObserver(this);
+}
+
+ShutdownObserver::~ShutdownObserver() {
+  WmShell::Get()->RemoveShellObserver(this);
+}
+
+void ShutdownObserver::OnAppTerminating() {
+  // Stop handling display configuration events once the shutdown
+  // process starts. crbug.com/177014.
+  display_configurator_->PrepareForExit();
+}
+
+}  // namespace ash