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 false;
   current_pos_ = current_pos;
   NoteLayerPropertyChanged();
   return true;
 }
 
 bool ScrollbarLayerImplBase::CanScrollOrientation() const {
   LayerImpl* scroll_layer = layer_tree_impl()->LayerById(scroll_layer_id_);
   if (!scroll_layer)
     return false;
+
+  float page_scale_factor = layer_tree_impl()->current_page_scale_factor();

[bokan, 2017/04/18 17:39:08]

I don't think this is right, why'd you add page scale from the previous patch?
The page scale factor is already applied as needed from UpdateScrollbars.
Further, it should only be applied for viewport scrollbars. This looked fine to
me in the previous patch.

+  float device_scale_factor = layer_tree_impl()->device_scale_factor();
+
+  int clip_layer_length =
+      std::ceil(clip_layer_length_ * page_scale_factor * device_scale_factor);
+  int scroll_layer_length =
+      std::ceil(scroll_layer_length_ * page_scale_factor * device_scale_factor);
+
   return scroll_layer->user_scrollable(orientation()) &&
-         clip_layer_length_ < 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 145 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