Add MD ink drop ripple to shelf app items

ash/shelf/ink_drop_button_listener.h

Index: ash/shelf/ink_drop_button_listener.h
diff --git a/ash/shelf/ink_drop_button_listener.h b/ash/shelf/ink_drop_button_listener.h
new file mode 100644
index 0000000000000000000000000000000000000000..6374c3e565aea04bdaaee4ec87bb1f1437d76314
--- /dev/null
+++ b/ash/shelf/ink_drop_button_listener.h
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+// 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_SHELF_INK_DROP_BUTTON_LISTENER_H_
+#define ASH_SHELF_INK_DROP_BUTTON_LISTENER_H_
+
+#include "ash/ash_export.h"
+
+namespace views {
+class Button;
+class InkDrop;
+}
+
+namespace ash {
+
+// An interface used by buttons on shelf to notify ShelfView when they are
+// pressed. |ink_drop| is used to do appropriate ink drop animation based on the
+// action performed.
+// TODO(mohsen): A better approach would be to return a value indicating the
+// type of action performed such that the button can animate the ink drop.
+// Currently, it is not possible because showing menu is synchronous and blocks
+// the call. Fix this after menu is converted to synchronous.  Long-term, the
+// return value can be merged into ButtonListener.
+class ASH_EXPORT InkDropButtonListener {
+ public:
+  virtual void ButtonPressed(views::Button* sender,
+                             const ui::Event& event,
+                             views::InkDrop* ink_drop) = 0;
+
+ protected:
+  virtual ~InkDropButtonListener() {}
+};
+
+}  // namespace ash
+
+#endif  // ASH_SHELF_INK_DROP_BUTTON_LISTENER_H_