[Chrome OS MD] Draw a 1px separator between 2 tray items

ash/common/system/view_observer.h

Index: ash/common/system/view_observer.h
diff --git a/ash/common/system/view_observer.h b/ash/common/system/view_observer.h
new file mode 100644
index 0000000000000000000000000000000000000000..8c6ce2c14285340e23b68d141d48c5780a3e3af4
--- /dev/null
+++ b/ash/common/system/view_observer.h
@@ -0,0 +1,27 @@
+// 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_VIEW_OBSERVER_H_
+#define ASH_COMMON_SYSTEM_VIEW_OBSERVER_H_
+
+#include "ash/ash_export.h"
+#include "base/macros.h"
+#include "ui/views/widget/widget.h"
+
+namespace ash {
+class TrayBackgroundView;
+
+class ASH_EXPORT ViewObserver {

[varkha, 2016/07/26 23:10:15]

This name seems too generic. Maybe TrayBackgroundViewVisibilityObserver?

+ public:
+  ViewObserver() {}
+
+  // Called when |tray| visibility changes.
+  virtual void OnVisibilityChange(TrayBackgroundView* tray) {}
+
+  DISALLOW_COPY_AND_ASSIGN(ViewObserver);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_SYSTEM_VIEW_OBSERVER_H_