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

ui/views/animation/test/test_ink_drop_hover_observer.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 UI_VIEWS_ANIMATION_TEST_TEST_INK_DROP_HOVER_OBSERVER_H_
+#define UI_VIEWS_ANIMATION_TEST_TEST_INK_DROP_HOVER_OBSERVER_H_
+
+#include "base/macros.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "ui/views/animation/ink_drop_hover.h"
+#include "ui/views/animation/ink_drop_hover_observer.h"
+#include "ui/views/animation/ink_drop_state.h"
+#include "ui/views/animation/test/test_ink_drop_animation_observer_helper.h"
+
+namespace views {
+namespace test {
+
+// Simple InkDropHoverObserver test double that tracks if InkDropHoverObserver
+// methods are invoked and the parameters used for the last invocation.
+class TestInkDropHoverObserver
+    : public InkDropHoverObserver,
+      public TestInkDropAnimationObserverHelper<InkDropHover::AnimationType> {
+ public:
+  TestInkDropHoverObserver();
+  ~TestInkDropHoverObserver() override = default;
+
+  void set_ink_drop_hover(InkDropHover* ink_drop_hover) {
+    ink_drop_hover_ = ink_drop_hover;
+  }
+
+  // InkDropHoverObserver:
+  void AnimationStarted(InkDropHover::AnimationType animation_type) override;
+  void AnimationEnded(InkDropHover::AnimationType animation_type,
+                      InkDropAnimationEndedReason reason) override;
+
+ private:
+  // The type this inherits from. Reduces verbosity in .cc file.
+  using ObserverHelper =
+      TestInkDropAnimationObserverHelper<InkDropHover::AnimationType>;
+
+  // An InkDropHover to spy info from when notifications are handled.
+  InkDropHover* ink_drop_hover_ = nullptr;
+
+  DISALLOW_COPY_AND_ASSIGN(TestInkDropHoverObserver);
+};
+
+}  // namespace test
+}  // namespace views
+
+#endif  // UI_VIEWS_ANIMATION_TEST_TEST_INK_DROP_HOVER_OBSERVER_H_