Return main thread scroll layer in FindScrollLayerForDeviceViewportPoint

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index 2bbf7825465110fb2f64438ac05817790f2ef71a..26892295d8816a191846de35b0a8dfb9d396a2ba 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -660,6 +660,9 @@ class CC_EXPORT LayerTreeHostImpl
       LayerImpl* layer_hit_by_point,
       bool* scroll_on_main_thread,
       uint32_t* main_thread_scrolling_reason) const;
+
+  LayerImpl* FindScrollLayerByLayer(LayerImpl* layer_impl) const;
+
   float DeviceSpaceDistanceToLayer(const gfx::PointF& device_viewport_point,
                                    LayerImpl* layer_impl);
   void StartScrollbarFadeRecursive(LayerImpl* layer);