Hide scrollbars when their dimensions are not scrollable.

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 5e5e279fa254ed1222791095d8506ada832853f8..8d93a5456c3849e4c2f557ed07d0a13295446f3d 100644
--- a/cc/layers/scrollbar_layer_impl_base.cc
+++ b/cc/layers/scrollbar_layer_impl_base.cc
@@ -122,6 +122,12 @@ bool ScrollbarLayerImplBase::SetMaximum(int maximum) {
   return true;
 }
 
+bool ScrollbarLayerImplBase::CanScrollOrientation() const {
+  if (!scroll_layer_)
+    return false;
+  return scroll_layer_->user_scrollable(orientation()) && (0 < maximum());
+}
+
 bool ScrollbarLayerImplBase::SetVerticalAdjust(float vertical_adjust) {
   if (vertical_adjust_ == vertical_adjust)
     return false;