chromeos: changes how DisplayManagerObservers are notified

ash/mus/display_synchronizer.h

Index: ash/mus/display_synchronizer.h
diff --git a/ash/mus/display_synchronizer.h b/ash/mus/display_synchronizer.h
new file mode 100644
index 0000000000000000000000000000000000000000..791fffe375504c396a8a8af9187d623b9e86dd59
--- /dev/null
+++ b/ash/mus/display_synchronizer.h
@@ -0,0 +1,40 @@
+// Copyright 2017 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_MUS_DISPLAY_SYNCHRONIZER_H_
+#define ASH_MUS_DISPLAY_SYNCHRONIZER_H_
+
+#include "ash/display/window_tree_host_manager.h"
+#include "base/macros.h"
+
+namespace aura {
+class WindowManagerClient;
+}
+
+namespace ash {
+
+// DisplaySynchronizer keeps the display state in mus in sync with ash's display
+// state. As ash controls the overall display state this synchronization is one
+// way (from ash to mus).
+class DisplaySynchronizer : public ash::WindowTreeHostManager::Observer {
+ public:
+  explicit DisplaySynchronizer(
+      aura::WindowManagerClient* window_manager_client);
+  ~DisplaySynchronizer() override;
+
+ private:
+  void SendDisplayConfigurationToServer();
+
+  // WindowTreeHostManager::Observer:
+  void OnDisplaysInitialized() override;
+  void OnDisplayConfigurationChanged() override;
+
+  aura::WindowManagerClient* window_manager_client_;
+
+  DISALLOW_COPY_AND_ASSIGN(DisplaySynchronizer);
+};
+
+}  // namespace ash
+
+#endif  // ASH_MUS_DISPLAY_SYNCHRONIZER_H_