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/base/math_util.h"
 #include "cc/trees/effect_node.h"
 #include "cc/trees/layer_tree_impl.h"
 #include "ui/gfx/geometry/rect_conversions.h"
 
 namespace cc {
 
 ScrollbarLayerImplBase::ScrollbarLayerImplBase(
     LayerTreeImpl* tree_impl,
     int id,
     ScrollbarOrientation orientation,
@@ skipping 42 matching lines @@
   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;
   return scroll_layer->user_scrollable(orientation()) &&
+         !MathUtil::IsFloatNearlyTheSame(clip_layer_length_,

[bokan, 2017/04/10 14:20:56]

Thinking about this some more: this limit is kind of arbitrary. How about this
instead: convert the clip and scroll sizes into device pixels using
layer_tree_impl_->device_scale_factor() and ceil that. In that case, we're not
losing anything since its impossible to scroll by less than a device pixel.

Not sure if we should ceil the scroll layer or floor it...I think it might not
matter as I expect that to always be a whole number.

+                                         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