change overlay scrollbar hover show to hover fade in

cc/input/scrollbar_animation_controller.h

 // Copyright 2012 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_H_
 #define CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_
 
 #include "base/cancelable_callback.h"
 #include "base/memory/weak_ptr.h"
 #include "base/time/time.h"
@@ skipping 35 matching lines @@
       base::TimeDelta fade_out_delay,
       base::TimeDelta fade_out_resize_delay,
       base::TimeDelta fade_out_duration);
 
   // ScrollbarAnimationController for Desktop Overlay Scrollbar. It has show &
   // fade out animation and thinning animation.
   static std::unique_ptr<ScrollbarAnimationController>
   CreateScrollbarAnimationControllerAuraOverlay(
       int scroll_layer_id,
       ScrollbarAnimationControllerClient* client,
-      base::TimeDelta show_delay,
+      base::TimeDelta fade_in_delay,
       base::TimeDelta fade_out_delay,
       base::TimeDelta fade_out_resize_delay,
+      base::TimeDelta fade_in_duration,
       base::TimeDelta fade_out_duration,
       base::TimeDelta thinning_duration);
 
   ~ScrollbarAnimationController();
 
   bool ScrollbarsHidden() const;
 
   bool Animate(base::TimeTicks now);
 
   // WillUpdateScroll expects to be called even if the scroll position won't
@@ skipping 17 matching lines @@
   void DidMouseMoveNear(ScrollbarOrientation, float);
 
   // Called when Blink wants to show the scrollbars (via
   // ScrollableArea::showOverlayScrollbars).
   void DidRequestShowFromMainThread();
 
   bool MouseIsOverScrollbar(ScrollbarOrientation orientation) const;
   bool MouseIsNearScrollbar(ScrollbarOrientation orientation) const;
   bool MouseIsNearAnyScrollbar() const;
 
-  static constexpr float kMouseMoveDistanceToTriggerShow = 30.0f;
+  static constexpr float kMouseMoveDistanceToTriggerFadeIn = 30.0f;
 
  private:
   ScrollbarAnimationController(int scroll_layer_id,
                                ScrollbarAnimationControllerClient* client,
                                base::TimeDelta fade_out_delay,
                                base::TimeDelta fade_out_resize_delay,
                                base::TimeDelta fade_out_duration);
 
   ScrollbarAnimationController(int scroll_layer_id,
                                ScrollbarAnimationControllerClient* client,
-                               base::TimeDelta show_delay,
+                               base::TimeDelta fade_in_delay,
                                base::TimeDelta fade_out_delay,
                                base::TimeDelta fade_out_resize_delay,
+                               base::TimeDelta fade_in_duration,
                                base::TimeDelta fade_out_duration,
                                base::TimeDelta thinning_duration);
 
   ScrollbarSet Scrollbars() const;
   SingleScrollbarAnimationControllerThinning& GetScrollbarAnimationController(
       ScrollbarOrientation) const;
 
   // Returns how far through the animation we are as a progress value from
   // 0 to 1.
   float AnimationProgressAtTime(base::TimeTicks now);
   void RunAnimationFrame(float progress);
 
   void StartAnimation();
   void StopAnimation();
 
   void Show();
 
-  void PostDelayedShow();
+  void PostDelayedFadeIn();
   void PostDelayedFadeOut(bool on_resize);
 
   bool Captured() const;
 
   bool CalcNeedTriggerScrollbarShow(ScrollbarOrientation orientation,
                                     float distance) const;
 
   void ApplyOpacityToScrollbars(float opacity);
 
+  // Describes whether the current animation should FadeIn or FadeOut.
+  enum AnimationChange { NONE, FADE_IN, FADE_OUT };
+
   ScrollbarAnimationControllerClient* client_;
 
   base::TimeTicks last_awaken_time_;
 
   // show_delay_ is only for the case where the mouse hovers near the screen

[bokan, 2017/04/13 15:31:40]

nit: update comment.

   // edge.
-  base::TimeDelta show_delay_;
+  base::TimeDelta fade_in_delay_;
   base::TimeDelta fade_out_delay_;
   base::TimeDelta fade_out_resize_delay_;
 
+  base::TimeDelta fade_in_duration_;
+  base::TimeDelta fade_out_duration_;
+
   bool need_trigger_scrollbar_show_;
 
   bool is_animating_;
+  AnimationChange animation_change_;
 
   const int scroll_layer_id_;
   bool currently_scrolling_;
   bool show_in_fast_scroll_;
 
-  base::CancelableClosure delayed_scrollbar_show_;
+  base::CancelableClosure delayed_scrollbar_fade_in_;
   base::CancelableClosure delayed_scrollbar_fade_out_;
 
   float opacity_;
-  base::TimeDelta fade_out_duration_;
 
   const bool show_scrollbars_on_scroll_gesture_;
   const bool need_thinning_animation_;
   std::unique_ptr<SingleScrollbarAnimationControllerThinning>
       vertical_controller_;
   std::unique_ptr<SingleScrollbarAnimationControllerThinning>
       horizontal_controller_;
 
   base::WeakPtrFactory<ScrollbarAnimationController> weak_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLLBAR_ANIMATION_CONTROLLER_H_