Add generic PaletteDelegate code.

ash/common/palette_delegate.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_COMMON_PALETTE_DELEGATE_H_
+#define ASH_COMMON_PALETTE_DELEGATE_H_
+
+#include "ash/ash_export.h"
+#include "base/macros.h"
+
+namespace ash {
+
+// This delegate allows the UI code in ash, e.g. |PaletteTray|, to perform
+// Chrome-specific actions.
+class PaletteDelegate {
+ public:
+  virtual ~PaletteDelegate() {}
+
+  // TODO(jdufault): This delegate will be implemented in later CLs.
+
+ private:
+  DISALLOW_ASSIGN(PaletteDelegate);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_PALETTE_DELEGATE_H_