Added material design mouse hover feedback support.

ui/views/animation/ink_drop_hover.h

+// Copyright 2015 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_INK_DROP_HOVER_H_
+#define UI_VIEWS_ANIMATION_INK_DROP_HOVER_H_
+
+#include "base/macros.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/time/time.h"
+#include "ui/gfx/geometry/point.h"
+#include "ui/gfx/geometry/size.h"
+#include "ui/views/views_export.h"
+
+namespace ui {
+class Layer;
+class CallbackLayerAnimationObserver;
+}  // namespace ui
+
+namespace views {
+class RoundedRectangleLayerDelegate;
+
+// Manages fade in/out animations for a painted Layer that is used to provide
+// visual feedback on ui::Views for mouse hover states.
+class VIEWS_EXPORT InkDropHover {
+ public:
+  InkDropHover(const gfx::Size& size, int corner_radius);
+  ~InkDropHover();
+
+  // Returns true if the hover layer is visible.
+  bool IsVisible() const;
+
+  // Fades in the hover visual over the given |duration|.
+  void FadeIn(const base::TimeDelta& duration);

[sadrul, 2015/11/04 19:58:11]

TimeDelta is a single int64, and we typically just send by value. (although now
that I look, we do use a const-ref in quite a few places ... hm)

[bruthig, 2015/11/11 21:48:44]

Seems like a reasonable abstraction to me :)

+
+  // Fades out the hover visual over the given |duration|.
+  void FadeOut(const base::TimeDelta& duration);
+
+  // The root Layer that can be added in to a Layer tree.
+  ui::Layer* root_layer() { return layer_.get(); }

[sadrul, 2015/11/04 19:58:11]

Why root_layer() instead of just layer()?

[bruthig, 2015/11/11 21:48:45]

Done.

+
+  // Sets the |center_point| of the hover layer relative to its parent Layer.
+  void SetCenterPoint(const gfx::Point& center_point);
+
+ private:
+  enum HoverAnimationType { FADE_IN, FADE_OUT };
+
+  // Animates a fade in/out as specified by |animation_type| over the given
+  // |duration|.
+  void AnimateFade(HoverAnimationType animation_type,
+                   const base::TimeDelta& duration);
+
+  // The callback that will be invoked when a fade in/out animation is complete.
+  bool AnimationEndedCallback(
+      HoverAnimationType animation_type,
+      const ui::CallbackLayerAnimationObserver& observer);
+
+  // The LayerDelegate that paints the hover |layer_|.
+  scoped_ptr<RoundedRectangleLayerDelegate> layer_delegate_;
+
+  // The visual hover layer that is painted by |layer_delegate_|.
+  scoped_ptr<ui::Layer> layer_;
+
+  DISALLOW_COPY_AND_ASSIGN(InkDropHover);
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_ANIMATION_INK_DROP_HOVER_H_