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 e9c5514d5f9022fd7c57c9466f7f7d2ba449a586..223ebe50c83b4e758705b16db152d4e3eafc0de4 100644
--- a/cc/layers/scrollbar_layer_impl_base.cc
+++ b/cc/layers/scrollbar_layer_impl_base.cc
@@ -70,8 +70,17 @@ 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();
+  float device_scale_factor = layer_tree_impl()->device_scale_factor();
+
+  int clip_device_pixels =
+      std::ceil(clip_layer_length_ * page_scale_factor * device_scale_factor);
+  int scroll_device_pixels =
+      std::ceil(scroll_layer_length_ * page_scale_factor * device_scale_factor);

[bokan, 2017/04/20 22:09:49]

We should floor scroll instead of ceil, see previous comment for why.

E.g.

DSF = 1
PSF = 2.3804
Clip = 49.99
Scroll = 50

So in DP:

Clip = 118.996196
Scroll = 119.02

So if we ceil both we'll get 119 < 120 which we clearly didn't intend.

+
   return scroll_layer->user_scrollable(orientation()) &&
-         clip_layer_length_ < scroll_layer_length_;
+         clip_device_pixels < scroll_device_pixels;
 }
 
 bool ScrollbarLayerImplBase::SetVerticalAdjust(float vertical_adjust) {