change overlay scrollbar hover show to hover fade in

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index da95603c411cd0f2f4c7d71393d1bfdff67f6756..5b8e5010ea69e7f67b1135034ba9aa95014c2dce 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -1468,29 +1468,26 @@ const gfx::Rect LayerTreeImpl::ViewportRectForTilePriority() const {
 
 std::unique_ptr<ScrollbarAnimationController>
 LayerTreeImpl::CreateScrollbarAnimationController(ElementId scroll_element_id) {
-  DCHECK(!settings().scrollbar_fade_out_delay.is_zero());
-  DCHECK(!settings().scrollbar_fade_out_duration.is_zero());
-  base::TimeDelta fade_out_delay = settings().scrollbar_fade_out_delay;
+  DCHECK(!settings().scrollbar_fade_delay.is_zero());
+  DCHECK(!settings().scrollbar_fade_duration.is_zero());
+  base::TimeDelta fade_delay = settings().scrollbar_fade_delay;
   base::TimeDelta fade_out_resize_delay =
       settings().scrollbar_fade_out_resize_delay;
-  base::TimeDelta fade_out_duration = settings().scrollbar_fade_out_duration;
+  base::TimeDelta fade_duration = settings().scrollbar_fade_duration;
   switch (settings().scrollbar_animator) {
     case LayerTreeSettings::ANDROID_OVERLAY: {
       return ScrollbarAnimationController::
           CreateScrollbarAnimationControllerAndroid(
-              scroll_element_id, layer_tree_host_impl_, fade_out_delay,
-              fade_out_resize_delay, fade_out_duration);
+              scroll_element_id, layer_tree_host_impl_, fade_delay,
+              fade_out_resize_delay, fade_duration);
     }
     case LayerTreeSettings::AURA_OVERLAY: {
-      DCHECK(!settings().scrollbar_show_delay.is_zero());
-      base::TimeDelta show_delay = settings().scrollbar_show_delay;
       base::TimeDelta thinning_duration =
           settings().scrollbar_thinning_duration;
       return ScrollbarAnimationController::
           CreateScrollbarAnimationControllerAuraOverlay(
-              scroll_element_id, layer_tree_host_impl_, show_delay,
-              fade_out_delay, fade_out_resize_delay, fade_out_duration,
-              thinning_duration);
+              scroll_element_id, layer_tree_host_impl_, fade_delay,
+              fade_out_resize_delay, fade_duration, thinning_duration);
     }
     case LayerTreeSettings::NO_ANIMATOR:
       NOTREACHED();