athena: Introduce ActivityView.

athena/activity/public/activity_view.h

+// Copyright 2014 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 ATHENA_ACTIVITY_PUBLIC_ACTIVITY_VIEW_H_
+#define ATHENA_ACTIVITY_PUBLIC_ACTIVITY_VIEW_H_
+
+#include "athena/athena_export.h"
+
+namespace athena {
+
+class ATHENA_EXPORT ActivityView {
+ public:
+  virtual ~ActivityView() {}
+
+  virtual void UpdateTitle() = 0;
+  virtual void UpdateIcon() = 0;
+  virtual void UpdateRepresentativeColor() = 0;
+};
+
+}  // namespace athena
+
+#endif  // ATHENA_ACTIVITY_PUBLIC_ACTIVITY_VIEW_H_