Revert of ash: Use system tray mojo interface to show system update tray icon

ash/common/system/update/update_observer.h

Index: ash/common/system/update/update_observer.h
diff --git a/ash/common/system/update/update_observer.h b/ash/common/system/update/update_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..3912f0dd0429cd9715471ee49e38fe4a6d1b03f8
--- /dev/null
+++ b/ash/common/system/update/update_observer.h
@@ -0,0 +1,23 @@
+// Copyright (c) 2012 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_COMMON_SYSTEM_UPDATE_UPDATE_OBSERVER_H_
+#define ASH_COMMON_SYSTEM_UPDATE_UPDATE_OBSERVER_H_
+
+#include "ash/ash_export.h"
+
+namespace ash {
+
+struct UpdateInfo;
+
+class ASH_EXPORT UpdateObserver {
+ public:
+  virtual ~UpdateObserver() {}
+
+  virtual void OnUpdateRecommended(const UpdateInfo& info) = 0;
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_SYSTEM_UPDATE_UPDATE_OBSERVER_H_