Remove DisplayChangeObserver ash dependencies.

ash/display/ash_display_string_provider.h

+// 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.
+
+#ifndef ASH_DISPLAY_ASH_DISPLAY_STRING_PROVIDER_H_
+#define ASH_DISPLAY_ASH_DISPLAY_STRING_PROVIDER_H_
+
+#include <string>
+
+#include "base/macros.h"
+#include "ui/display/manager/display_string_provider.h"
+
+namespace ash {
+
+class AshDisplayStringProvider : public display::DisplayStringProvider {
+ public:
+  AshDisplayStringProvider() {}
+  ~AshDisplayStringProvider() override {}
+
+  std::string GetInternalDisplayNameString() override;
+  std::string GetVirtualDisplayNameString() override;
+  std::string GetUnknownDisplayNameString() override;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(AshDisplayStringProvider);
+};
+
+}  // namespace ash
+
+#endif  // ASH_DISPLAY_ASH_DISPLAY_STRING_PROVIDER_H_