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 56e1d0cf2f8b298b74bc3d58a3e327a226e7b8e8..28e2d1977fedade5aebff68f81844c4352264f09 100644
--- a/cc/blink/web_layer_impl.cc
+++ b/cc/blink/web_layer_impl.cc
@@ -330,6 +330,12 @@ void WebLayerImpl::addMainThreadScrollingReasons(
   layer_->AddMainThreadScrollingReasons(main_thread_scrolling_reasons);
 }
 
+void WebLayerImpl::clearMainThreadScrollingReasons(
+    uint32_t main_thread_scrolling_reasons_to_clear) {
+  layer_->ClearMainThreadScrollingReasons(
+      main_thread_scrolling_reasons_to_clear);
+}
+
 void WebLayerImpl::clearMainThreadScrollingReasons() {
   layer_->ClearMainThreadScrollingReasons();
 }