Wheel scroll latching enabled behind flag.

content/browser/renderer_host/input/mouse_wheel_event_queue.cc

Index: content/browser/renderer_host/input/mouse_wheel_event_queue.cc
diff --git a/content/browser/renderer_host/input/mouse_wheel_event_queue.cc b/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
index d1d3bc22276279290e8cde1271e27591b76b26e3..70079e23308d10f1eeb85399332afa5a9555cc78 100644
--- a/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
+++ b/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
@@ -34,13 +34,16 @@ class QueuedWebMouseWheelEvent : public MouseWheelEventWithLatencyInfo {
 };
 
 MouseWheelEventQueue::MouseWheelEventQueue(MouseWheelEventQueueClient* client,
-                                           int64_t scroll_transaction_ms)
+                                           bool touchpad_scroll_latching)
     : client_(client),
       needs_scroll_begin_(true),
       needs_scroll_end_(false),
-      scroll_transaction_ms_(scroll_transaction_ms),
+      touchpad_scroll_latching_(touchpad_scroll_latching),
       scrolling_device_(blink::WebGestureDeviceUninitialized) {
   DCHECK(client);
+  scroll_transaction_ms_ = touchpad_scroll_latching
+                               ? kDefaultWheelScrollLatchingTransactionMs
+                               : kDefaultWheelScrollTransactionMs;

[tdresser, 2016/07/22 15:43:15]

I'm a bit confused here. Scroll transactions only matter for latching, so I'm
not sure what the difference between these constants is.

[sahel, 2016/07/25 15:54:53]

If the flag is enabled, wheel scroll latching will also happen.

 }
 
 MouseWheelEventQueue::~MouseWheelEventQueue() {
@@ -169,7 +172,7 @@ void MouseWheelEventQueue::ProcessMouseWheelAck(
       if (needs_scroll_begin_) {
         // If no GSB has been sent, it will be a non-synthetic GSB.
         SendScrollBegin(scroll_update, false);
-      } else if (has_phase_info) {
+      } else if (has_phase_info && !touchpad_scroll_latching_) {
         // If a GSB has been sent, generate a synthetic GSB if we have phase
         // information. This should be removed once crbug.com/526463 is fully
         // implemented.
@@ -192,7 +195,8 @@ void MouseWheelEventQueue::ProcessMouseWheelAck(
         // 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);
+        if (!touchpad_scroll_latching_)
+          SendScrollEnd(scroll_update, true);
       } else {
         scroll_end_timer_.Start(
             FROM_HERE,