MouseWheelEventQueue sends scrollEnd right away when latching is disabled.

content/browser/renderer_host/input/mouse_wheel_event_queue.cc

 // Copyright 2016 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 "content/browser/renderer_host/input/mouse_wheel_event_queue.h"
 
 #include "base/memory/ptr_util.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/trace_event/trace_event.h"
 #include "ui/events/base_event_utils.h"
@@ skipping 228 matching lines @@
         if (current_phase_ended) {
           // Non-synthetic GSEs are sent when the current phase is canceled or
           // ended.
           SendScrollEnd(scroll_update, false);
         } else if (has_phase_info) {
           // Generate a synthetic GSE for every update to force hit testing so
           // that the non-latching behavior is preserved. Remove once
           // crbug.com/526463 is fully implemented.
           SendScrollEnd(scroll_update, true);
         } else if (!has_phase_info) {
-          scroll_end_timer_.Start(
-              FROM_HERE,
-              base::TimeDelta::FromMilliseconds(scroll_transaction_ms_),
-              base::Bind(&MouseWheelEventQueue::SendScrollEnd,
-                         base::Unretained(this), scroll_update, false));
+          DCHECK_EQ(0, scroll_transaction_ms_);
+          SendScrollEnd(scroll_update, false);
         }
       }
     }
   }
 
   event_sent_for_gesture_ack_.reset();
   TryForwardNextEventToRenderer();
 }
 
 void MouseWheelEventQueue::OnGestureScrollEvent(
@@ skipping 84 matching lines @@
   scroll_begin.data.scrollBegin.deltaHintUnits =
       gesture_update.data.scrollUpdate.deltaUnits;
 
   needs_scroll_begin_ = false;
   needs_scroll_end_ = true;
   client_->ForwardGestureEventWithLatencyInfo(
       scroll_begin, ui::LatencyInfo(ui::SourceEventType::WHEEL));
 }
 
 }  // namespace content