Wheel scroll latching enabled 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/metrics/histogram_macros.h"
 #include "base/stl_util.h"
 #include "base/trace_event/trace_event.h"
 #include "content/common/input/web_input_event_traits.h"
@@ skipping 16 matching lines @@
 
   ~QueuedWebMouseWheelEvent() {
     TRACE_EVENT_ASYNC_END0("input", "MouseWheelEventQueue::QueueEvent", this);
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(QueuedWebMouseWheelEvent);
 };
 
 MouseWheelEventQueue::MouseWheelEventQueue(MouseWheelEventQueueClient* client,
-                                           int64_t scroll_transaction_ms)
+                                           bool enable_scroll_latching)
     : client_(client),
       needs_scroll_begin_(true),
       needs_scroll_end_(false),
-      scroll_transaction_ms_(scroll_transaction_ms),
+      enable_scroll_latching_(enable_scroll_latching),
       scrolling_device_(blink::WebGestureDeviceUninitialized) {
   DCHECK(client);
+  scroll_transaction_ms_ =
+      enable_scroll_latching_ ? kDefaultWheelScrollLatchingTransactionMs : 0;
 }
 
 MouseWheelEventQueue::~MouseWheelEventQueue() {
   if (!wheel_queue_.empty())
     base::STLDeleteElements(&wheel_queue_);
 }
 
 void MouseWheelEventQueue::QueueEvent(
     const MouseWheelEventWithLatencyInfo& event) {
   TRACE_EVENT0("input", "MouseWheelEventQueue::QueueEvent");
@@ skipping 230 matching lines @@
   scroll_begin.data.scrollBegin.targetViewport = false;
   scroll_begin.data.scrollBegin.deltaHintUnits =
       gesture_update.data.scrollUpdate.deltaUnits;
 
   needs_scroll_begin_ = false;
   needs_scroll_end_ = true;
   client_->ForwardGestureEventWithLatencyInfo(scroll_begin, ui::LatencyInfo());
 }
 
 }  // namespace content