Ignore rounding error between clip_layer_length_ and scroll_layer_length_

cc/layers/scrollbar_layer_impl_base.cc

Index: cc/layers/scrollbar_layer_impl_base.cc
diff --git a/cc/layers/scrollbar_layer_impl_base.cc b/cc/layers/scrollbar_layer_impl_base.cc
index da53036fea0a07cd555c932d769ce32092f6aa19..b3d4354211cfcc429a543ddbbf0c1dd8627263c7 100644
--- a/cc/layers/scrollbar_layer_impl_base.cc
+++ b/cc/layers/scrollbar_layer_impl_base.cc
@@ -5,6 +5,7 @@
 #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"
@@ -67,6 +68,8 @@ bool ScrollbarLayerImplBase::CanScrollOrientation() const {
   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_;
 }