Change the distance trigger scrollbar show

cc/input/scrollbar_animation_controller.cc

Index: cc/input/scrollbar_animation_controller.cc
diff --git a/cc/input/scrollbar_animation_controller.cc b/cc/input/scrollbar_animation_controller.cc
index 5c3434b0299f4624d7f49ca22bad6adb3f095bf6..c018016c8d7f93be8c052b088abf5e6fef919cfd 100644
--- a/cc/input/scrollbar_animation_controller.cc
+++ b/cc/input/scrollbar_animation_controller.cc
@@ -324,8 +324,7 @@ bool ScrollbarAnimationController::CalcNeedTriggerScrollbarShow(
     if (scrollbar->orientation() != orientation)
       continue;
 
-    if (distance <
-        (kMouseMoveDistanceToTriggerShow - scrollbar->ThumbThickness()))
+    if (distance < kMouseMoveDistanceToTriggerShow)
       return true;
   }