Change the distance trigger scrollbar show

cc/input/scrollbar_animation_controller.cc

 // Copyright 2014 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.
 
 #include "cc/input/scrollbar_animation_controller.h"
 
 #include <algorithm>
 
 #include "base/time/time.h"
 #include "cc/trees/layer_tree_impl.h"
@@ skipping 306 matching lines @@
   DCHECK(need_thinning_animation_);
 
   if (vertical_controller_->mouse_is_over_scrollbar() ||
       horizontal_controller_->mouse_is_over_scrollbar())
     return true;
 
   for (ScrollbarLayerImplBase* scrollbar : Scrollbars()) {
     if (scrollbar->orientation() != orientation)
       continue;
 
-    if (distance <
-        (kMouseMoveDistanceToTriggerShow - scrollbar->ThumbThickness()))
+    if (distance < kMouseMoveDistanceToTriggerShow)
       return true;
   }
 
   return false;
 }
 
 bool ScrollbarAnimationController::MouseIsOverScrollbar(
     ScrollbarOrientation orientation) const {
   DCHECK(need_thinning_animation_);
   return GetScrollbarAnimationController(orientation).mouse_is_over_scrollbar();
@@ skipping 39 matching lines @@
   if (opacity_ != opacity)
     client_->SetNeedsRedrawForScrollbarAnimation();
 
   opacity_ = opacity;
 
   if (previouslyVisible != currentlyVisible)
     client_->DidChangeScrollbarVisibility();
 }
 
 }  // namespace cc