Ignore rounding error between clip_layer_length_ and scroll_layer_length_

cc/layers/scrollbar_layer_impl_base.cc

 // 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.
 
 #include "cc/layers/scrollbar_layer_impl_base.h"
 
 #include <algorithm>
 #include "cc/trees/effect_node.h"
 #include "cc/trees/layer_tree_impl.h"
 #include "ui/gfx/geometry/rect_conversions.h"
@@ skipping 48 matching lines @@
   return true;
 }
 
 bool ScrollbarLayerImplBase::CanScrollOrientation() const {
   // TODO(pdr): Refactor this to not depend on layers by using the associated
   // scroll node's user_scrollable values.
   LayerImpl* scroll_layer =
       layer_tree_impl()->LayerByElementId(scroll_element_id_);
   if (!scroll_layer)
     return false;
+
   return scroll_layer->user_scrollable(orientation()) &&
+         !MathUtil::IsFloatNearlyTheSame(clip_layer_length_,

[enne (OOO), 2017/04/21 22:54:33]

Can you leave a comment here about why you need this check, and that the
intended behavior is not to show the scrollbar when there's a rounding error and
these are nearly the same?

+                                         scroll_layer_length_) &&
          clip_layer_length_ < scroll_layer_length_;
 }
 
 bool ScrollbarLayerImplBase::SetVerticalAdjust(float vertical_adjust) {
   if (vertical_adjust_ == vertical_adjust)
     return false;
   vertical_adjust_ = vertical_adjust;
   NoteLayerPropertyChanged();
   return true;
 }
@@ skipping 146 matching lines @@
   layer_tree_impl()->AddToOpacityAnimationsMap(id(), opacity);
 
   node->opacity = opacity;
   node->effect_changed = true;
   property_trees->changed = true;
   property_trees->effect_tree.set_needs_update(true);
   layer_tree_impl()->set_needs_update_draw_properties();
 }
 
 }  // namespace cc