Add MD Ink Drop Layers to InkDropHost only when a ripple/hover is active.

ui/views/animation/test/test_ink_drop_hover_observer.cc

+// 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.
+
+#include "ui/views/animation/test/test_ink_drop_hover_observer.h"
+
+#include "ui/views/animation/ink_drop_hover.h"
+
+namespace views {
+namespace test {
+
+TestInkDropHoverObserver::TestInkDropHoverObserver() {}
+
+void TestInkDropHoverObserver::AnimationStarted(
+    InkDropHover::AnimationType animation_type) {
+  ObserverHelper::OnAnimationStarted(animation_type);
+}
+
+void TestInkDropHoverObserver::AnimationEnded(
+    InkDropHover::AnimationType animation_type,
+    InkDropAnimationEndedReason reason) {
+  ObserverHelper::OnAnimationEnded(animation_type, reason);
+}
+
+}  // namespace test
+}  // namespace views