Remove DisplayChangeObserver ash dependencies.

ash/display/ash_display_string_provider.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/ash_display_string_provider.h"
+
+#include "ash/common/strings/grit/ash_strings.h"
+#include "ui/base/l10n/l10n_util.h"
+
+namespace ash {
+
+std::string AshDisplayStringProvider::GetInternalDisplayNameString() {
+  return l10n_util::GetStringUTF8(IDS_ASH_INTERNAL_DISPLAY_NAME);
+}
+
+std::string AshDisplayStringProvider::GetVirtualDisplayNameString() {
+  return l10n_util::GetStringUTF8(IDS_ASH_VIRTUAL_DISPLAY_NAME);
+}
+
+std::string AshDisplayStringProvider::GetUnknownDisplayNameString() {
+  return l10n_util::GetStringUTF8(IDS_ASH_STATUS_TRAY_UNKNOWN_DISPLAY_NAME);
+}
+
+}  // namespace ash