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..7e7f67647084abeb659804e9757b508c05f5d95e 100644
--- a/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
+++ b/content/browser/renderer_host/input/mouse_wheel_event_queue.cc
@@ -41,6 +41,8 @@ MouseWheelEventQueue::MouseWheelEventQueue(MouseWheelEventQueueClient* client,
       scroll_transaction_ms_(scroll_transaction_ms),
       scrolling_device_(blink::WebGestureDeviceUninitialized) {
   DCHECK(client);
+  touchpad_scroll_latching_ =

[ericrk, 2016/07/19 20:21:51]

nit: it seems odd/fragile to set this variable based on comparison with
scroll_transaction_ms_... might it be cleaner to pass in "bool
touchpad_scroll_latching" and then set the scroll_transaction_ms_ based on that
in the constructor?

[sahel, 2016/07/19 22:47:03]

Done.

+      scroll_transaction_ms_ == kDefaultWheelScrollTransactionMs ? false : true;
 }
 
 MouseWheelEventQueue::~MouseWheelEventQueue() {
@@ -169,7 +171,7 @@ 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 +194,8 @@ 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,