MacViews: Reveal scrollbars when resting on the trackpad.

ui/events/event.cc

Index: ui/events/event.cc
diff --git a/ui/events/event.cc b/ui/events/event.cc
index e82747ba32183cca73e95264af1af5345ebc8051..dc212a5faa902d6c09284c8a24d7cea4a1a61ed9 100644
--- a/ui/events/event.cc
+++ b/ui/events/event.cc
@@ -1388,13 +1388,15 @@ ScrollEvent::ScrollEvent(EventType type,
                          float y_offset,
                          float x_offset_ordinal,
                          float y_offset_ordinal,
-                         int finger_count)
+                         int finger_count,
+                         EventMomentumPhase momentum_phase)
     : MouseEvent(type, location, location, time_stamp, flags, 0),
       x_offset_(x_offset),
       y_offset_(y_offset),
       x_offset_ordinal_(x_offset_ordinal),
       y_offset_ordinal_(y_offset_ordinal),
-      finger_count_(finger_count) {
+      finger_count_(finger_count),
+      momentum_phase_(momentum_phase) {
   CHECK(IsScrollEvent());
   latency()->set_source_event_type(ui::SourceEventType::WHEEL);
 }