Ignore the rest of the scroll sequence if GSB is ignored.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2755 matching lines @@
     ScrollNode* scrolling_node,
     InputHandler::ScrollInputType type) {
   DCHECK(scroll_state);
   DCHECK(scroll_state->delta_x() == 0 && scroll_state->delta_y() == 0);
 
   InputHandler::ScrollStatus scroll_status;
   scroll_status.main_thread_scrolling_reasons =
       MainThreadScrollingReason::kNotScrollingOnMain;
   if (!scrolling_node) {
     scroll_status.thread = SCROLL_IGNORED;
+    if (settings_.is_layer_tree_for_subframe)
+      scroll_status.thread = SCROLL_UNKNOWN;
     scroll_status.main_thread_scrolling_reasons =
         MainThreadScrollingReason::kNoScrollingLayer;
     return scroll_status;
   }
   scroll_status.thread = SCROLL_ON_IMPL_THREAD;
   mutator_host_->ScrollAnimationAbort();
 
   browser_controls_offset_manager_->ScrollBegin();
 
   active_tree_->SetCurrentlyScrollingNode(scrolling_node);
@@ skipping 1523 matching lines @@
 
 void LayerTreeHostImpl::ShowScrollbarsForImplScroll(ElementId element_id) {
   if (!element_id)
     return;
   if (ScrollbarAnimationController* animation_controller =
           ScrollbarAnimationControllerForElementId(element_id))
     animation_controller->DidScrollUpdate();
 }
 
 }  // namespace cc