Hide scrollbars when their dimensions are not scrollable.

cc/layers/scrollbar_layer_impl_base.h

Index: cc/layers/scrollbar_layer_impl_base.h
diff --git a/cc/layers/scrollbar_layer_impl_base.h b/cc/layers/scrollbar_layer_impl_base.h
index a98c3ea5622284201580ae6b51e09126aa2af644..91cff32e248699029565c1ea40d057bb8db51ea3 100644
--- a/cc/layers/scrollbar_layer_impl_base.h
+++ b/cc/layers/scrollbar_layer_impl_base.h
@@ -44,6 +44,8 @@ class CC_EXPORT ScrollbarLayerImplBase : public LayerImpl {
     return is_left_side_vertical_scrollbar_;
   }
 
+  bool can_scroll_orientation() const;
+
   virtual void PushPropertiesTo(LayerImpl* layer) override;
   virtual ScrollbarLayerImplBase* ToScrollbarLayer() override;
   void PushScrollClipPropertiesTo(LayerImpl* layer);