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

cc/layers/layer.cc

Index: cc/layers/layer.cc
diff --git a/cc/layers/layer.cc b/cc/layers/layer.cc
index 24ae93291ebf13f2f225c3c6231e8f084b03b736..26bea9b61dff16486ff9adfe8c3a61334f23dc1d 100644
--- a/cc/layers/layer.cc
+++ b/cc/layers/layer.cc
@@ -960,6 +960,15 @@ void Layer::AddMainThreadScrollingReasons(
   SetNeedsCommit();
 }
 
+void Layer::ClearMainThreadScrollingReasons(
+    uint32_t main_thread_scrolling_reasons_to_clear) {
+  DCHECK(IsPropertyChangeAllowed());
+  DCHECK(main_thread_scrolling_reasons_to_clear);
+  main_thread_scrolling_reasons_ =
+      ~main_thread_scrolling_reasons_to_clear & main_thread_scrolling_reasons_;
+  SetNeedsCommit();
+}
+
 void Layer::ClearMainThreadScrollingReasons() {
   DCHECK(IsPropertyChangeAllowed());
   if (!main_thread_scrolling_reasons_)