Track whether a scroll sequence has been partially prevented

content/common/input/web_input_event_traits.cc

Index: content/common/input/web_input_event_traits.cc
diff --git a/content/common/input/web_input_event_traits.cc b/content/common/input/web_input_event_traits.cc
index 4515dceb69f4a47f8f6536cc53e69189f5c9b08c..087cf61e0cf2e8869c73ba55f03c4af33b102489 100644
--- a/content/common/input/web_input_event_traits.cc
+++ b/content/common/input/web_input_event_traits.cc
@@ -267,6 +267,9 @@ void Coalesce(const WebGestureEvent& event_to_coalesce,
         event_to_coalesce.data.scrollUpdate.deltaX;
     event->data.scrollUpdate.deltaY +=
         event_to_coalesce.data.scrollUpdate.deltaY;
+    DCHECK_EQ(
+        event->data.scrollUpdate.previousUpdateInSequencePrevented,
+        event_to_coalesce.data.scrollUpdate.previousUpdateInSequencePrevented);
   } else if (event->type == WebInputEvent::GesturePinchUpdate) {
     event->data.pinchUpdate.scale *= event_to_coalesce.data.pinchUpdate.scale;
     // Ensure the scale remains bounded above 0 and below Infinity so that