Implement fade-out animation for Aura overlay scrollbars (CC only).

cc/input/scrollbar_animation_controller_thinning.h

 // Copyright 2013 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 CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_
 #define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "cc/base/cc_export.h"
 #include "cc/input/scrollbar_animation_controller.h"
 
 namespace cc {
 class LayerImpl;
 
 // Scrollbar animation that partially fades and thins after an idle delay,
 // and reacts to mouse movements.
 class CC_EXPORT ScrollbarAnimationControllerThinning
     : public ScrollbarAnimationController {
  public:
   static std::unique_ptr<ScrollbarAnimationControllerThinning> Create(
       int scroll_layer_id,
       ScrollbarAnimationControllerClient* client,
       base::TimeDelta delay_before_starting,
       base::TimeDelta resize_delay_before_starting,
-      base::TimeDelta duration);
+      base::TimeDelta fade_duration,
+      base::TimeDelta thinning_duration);
 
   ~ScrollbarAnimationControllerThinning() override;
 
   void set_mouse_move_distance_for_test(float distance) {
     mouse_move_distance_to_trigger_animation_ = distance;
   }
   bool mouse_is_over_scrollbar() const { return mouse_is_over_scrollbar_; }
   bool mouse_is_near_scrollbar() const { return mouse_is_near_scrollbar_; }
 
   void DidScrollUpdate(bool on_resize) override;
 
   void DidCaptureScrollbarBegin() override;
   void DidCaptureScrollbarEnd() override;
   void DidMouseMoveOffScrollbar() override;
   void DidMouseMoveNear(float distance) override;
 
  protected:
   ScrollbarAnimationControllerThinning(
       int scroll_layer_id,
       ScrollbarAnimationControllerClient* client,
       base::TimeDelta delay_before_starting,
       base::TimeDelta resize_delay_before_starting,
-      base::TimeDelta duration);
+      base::TimeDelta fade_duration,
+      base::TimeDelta thinning_duration);
 
   void RunAnimationFrame(float progress) override;
 
  private:
-  // Describes whether the current animation should INCREASE (darken / thicken)
-  // a bar or DECREASE it (lighten / thin).
+  // Describes whether the current animation should INCREASE (thicken)
+  // a bar or DECREASE it (thin).
   enum AnimationChange { NONE, INCREASE, DECREASE };
-  float OpacityAtAnimationProgress(float progress);
-  float ThumbThicknessScaleAtAnimationProgress(float progress);
+  enum AnimatingProperty { OPACITY, THICKNESS };
+  float ThumbThicknessScaleAt(float progress);
   float AdjustScale(float new_value,
                     float current_value,
                     AnimationChange animation_change,
                     float min_value,
                     float max_value);
-  void ApplyOpacityAndThumbThicknessScale(float opacity,
-                                          float thumb_thickness_scale);
+  void ApplyOpacity(float opacity);
+  void ApplyThumbThicknessScale(float thumb_thickness_scale);
 
+  void SetCurrentAnimatingProperty(AnimatingProperty property);
+
+  bool is_visible_;

[aelias_OOO_until_Jul13, 2016/10/20 23:40:51]

Hmm, I don't generally like "visible" booleans due to their many possible subtle
meanings.  Could you just store "float opacity" and check "if (opacity == 0.0f)"
in the various places?

[bokan, 2016/10/21 00:32:30]

Done.

   bool captured_;
   bool mouse_is_over_scrollbar_;
   bool mouse_is_near_scrollbar_;
   // Are we narrowing or thickening the bars.
   AnimationChange thickness_change_;
-  // Are we darkening or lightening the bars.
-  AnimationChange opacity_change_;
   // How close should the mouse be to the scrollbar before we thicken it.
   float mouse_move_distance_to_trigger_animation_;
 
+  base::TimeDelta fade_duration_;
+  base::TimeDelta thinning_duration_;
+
+  AnimatingProperty current_animating_property_;
+
   DISALLOW_COPY_AND_ASSIGN(ScrollbarAnimationControllerThinning);
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_THINNING_H_