Touchpad and wheel scroll latching for ChromeOS behind flag.

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 260 matching lines @@
       scroll_end_timer_.Reset();
       task.Run();
     }
     scrolling_device_ = gesture_event.event.sourceDevice;
   } else if (scrolling_device_ == gesture_event.event.sourceDevice &&
              (gesture_event.event.type ==
                   blink::WebInputEvent::GestureScrollEnd ||
               gesture_event.event.type ==
                   blink::WebInputEvent::GestureFlingStart)) {
     scrolling_device_ = blink::WebGestureDeviceUninitialized;
-    if (scroll_end_timer_.IsRunning())
-      scroll_end_timer_.Reset();
+    if (scroll_end_timer_.IsRunning()) {
+      if (enable_scroll_latching_) {
+        // Don't send the pending ScrollEnd if a fling is happening.
+        // The next wheel event will still need a ScrollBegin.
+        scroll_end_timer_.Stop();
+        needs_scroll_begin_ = true;
+        needs_scroll_end_ = false;
+      } else {
+        scroll_end_timer_.Reset();
+      }
+    }
   }
 }
 
 void MouseWheelEventQueue::TryForwardNextEventToRenderer() {
   TRACE_EVENT0("input", "MouseWheelEventQueue::TryForwardNextEventToRenderer");
 
   if (wheel_queue_.empty() || event_sent_for_gesture_ack_)
     return;
 
   event_sent_for_gesture_ack_ = std::move(wheel_queue_.front());
@@ skipping 46 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