Wheel scroll latching enabled behind flag.

cc/trees/layer_tree_host_impl.cc

Index: cc/trees/layer_tree_host_impl.cc
diff --git a/cc/trees/layer_tree_host_impl.cc b/cc/trees/layer_tree_host_impl.cc
index e6db70e6cbf14ee4bb5643da1ca6ed8efd3569dc..2a9e01ff2c265eb162282cc9bd68659b134eae0f 100644
--- a/cc/trees/layer_tree_host_impl.cc
+++ b/cc/trees/layer_tree_host_impl.cc
@@ -2684,8 +2684,12 @@ InputHandler::ScrollStatus LayerTreeHostImpl::ScrollBegin(
   ScrollStatus scroll_status;
   scroll_status.main_thread_scrolling_reasons =
       MainThreadScrollingReason::kNotScrollingOnMain;
+
   TRACE_EVENT0("cc", "LayerTreeHostImpl::ScrollBegin");
 
+  if (scroll_state->is_in_inertial_phase())
+    return FlingScrollBegin();
+
   ClearCurrentlyScrollingLayer();
 
   gfx::Point viewport_point(scroll_state->position_x(),
@@ -3238,7 +3242,13 @@ void LayerTreeHostImpl::ScrollEnd(ScrollState* scroll_state) {
 
   DistributeScrollDelta(scroll_state);
   top_controls_manager_->ScrollEnd();
-  ClearCurrentlyScrollingLayer();
+
+  if (scroll_state->is_in_inertial_phase()) {
+    // There might be a fling after the scroll end. In those cases,
+    // don't clear the currently scrolling layer to avoid a new hit test for the
+    // fling.
+    ClearCurrentlyScrollingLayer();
+  }
 }
 
 InputHandler::ScrollStatus LayerTreeHostImpl::FlingScrollBegin() {