Fix smooth scroll jump when switching scroll handling between MT and CC

cc/blink/web_layer_impl.cc

Index: cc/blink/web_layer_impl.cc
diff --git a/cc/blink/web_layer_impl.cc b/cc/blink/web_layer_impl.cc
index ca63d15fc96f363cde745a77c1c85bb5d80f7a75..da2c83e5f305d3218b833e3ff447eea57c02aa4a 100644
--- a/cc/blink/web_layer_impl.cc
+++ b/cc/blink/web_layer_impl.cc
@@ -330,8 +330,14 @@ void WebLayerImpl::addMainThreadScrollingReasons(
   layer_->AddMainThreadScrollingReasons(main_thread_scrolling_reasons);
 }
 
-void WebLayerImpl::clearMainThreadScrollingReasons() {
-  layer_->ClearMainThreadScrollingReasons();
+void WebLayerImpl::clearMainThreadScrollingReasons(
+    uint32_t main_thread_scrolling_reasons_to_clear) {
+  layer_->ClearMainThreadScrollingReasons(
+      main_thread_scrolling_reasons_to_clear);
+}
+
+uint32_t WebLayerImpl::mainThreadScrollingReasons() {
+  return layer_->main_thread_scrolling_reasons();
 }
 
 bool WebLayerImpl::shouldScrollOnMainThread() const {