Forward GestureFlingStart in OOPIF, re-enable DCHECK.

content/browser/renderer_host/render_widget_host_input_event_router.cc

Index: content/browser/renderer_host/render_widget_host_input_event_router.cc
diff --git a/content/browser/renderer_host/render_widget_host_input_event_router.cc b/content/browser/renderer_host/render_widget_host_input_event_router.cc
index 7f11483bd5fa7eb8b92a9189357d13943070e64a..7baa7855193d2e4db8c6a9e73d6087d837b90527 100644
--- a/content/browser/renderer_host/render_widget_host_input_event_router.cc
+++ b/content/browser/renderer_host/render_widget_host_input_event_router.cc
@@ -556,7 +556,8 @@ void RenderWidgetHostInputEventRouter::BubbleScrollEvent(
   // including bubbling, based on GestureScrollBegin.
   DCHECK(target_view);
   DCHECK(event.GetType() == blink::WebInputEvent::kGestureScrollUpdate ||
-         event.GetType() == blink::WebInputEvent::kGestureScrollEnd);
+         event.GetType() == blink::WebInputEvent::kGestureScrollEnd ||
+         event.GetType() == blink::WebInputEvent::kGestureFlingStart);
   // DCHECK_XNOR the current and original bubble targets. Both should be set
   // if a bubbling gesture scroll is in progress.
   DCHECK(!first_bubbling_scroll_target_.target ==
@@ -570,7 +571,8 @@ void RenderWidgetHostInputEventRouter::BubbleScrollEvent(
   if (target_view == first_bubbling_scroll_target_.target) {
     bubbling_gesture_scroll_target_.target->ProcessGestureEvent(event,
                                                                 latency_info);
-    if (event.GetType() == blink::WebInputEvent::kGestureScrollEnd) {
+    if (event.GetType() == blink::WebInputEvent::kGestureScrollEnd ||
+        event.GetType() == blink::WebInputEvent::kGestureFlingStart) {
       first_bubbling_scroll_target_.target = nullptr;
       bubbling_gesture_scroll_target_.target = nullptr;
     }