ui::GestureProvider gives GestureEventData the number of touch points.

ui/events/gesture_detection/touch_disposition_gesture_filter.cc

Index: ui/events/gesture_detection/touch_disposition_gesture_filter.cc
diff --git a/ui/events/gesture_detection/touch_disposition_gesture_filter.cc b/ui/events/gesture_detection/touch_disposition_gesture_filter.cc
index 6f405e58f96faa00f18fbe1fe1c62c8ae17bcbf5..009c21d7fd3e653136c49d51949a8eae474076ab 100644
--- a/ui/events/gesture_detection/touch_disposition_gesture_filter.cc
+++ b/ui/events/gesture_detection/touch_disposition_gesture_filter.cc
@@ -15,12 +15,15 @@ namespace {
 COMPILE_ASSERT(ET_GESTURE_TYPE_END - ET_GESTURE_TYPE_START < 32,
                gesture_type_count_too_large);
 
-GestureEventData CreateGesture(EventType type, int motion_event_id) {
+GestureEventData CreateGesture(EventType type,
+                               int motion_event_id,
+                               int touch_point_count) {
   return GestureEventData(type,
                           motion_event_id,
                           base::TimeTicks(),
                           0,
                           0,
+                          touch_point_count,
                           GestureEventDetails(type, 0, 0));
 }
 
@@ -270,7 +273,7 @@ void TouchDispositionGestureFilter::CancelTapIfNecessary() {
     return;
 
   SendGesture(
-      CreateGesture(ET_GESTURE_TAP_CANCEL, ending_event_motion_event_id_));
+      CreateGesture(ET_GESTURE_TAP_CANCEL, ending_event_motion_event_id_, 1));

[jdduke (slow), 2014/04/09 16:53:05]

I don't think we'll ever generate a touch count > 1, so let's have the utility
method supply that.

[tdresser, 2014/04/09 18:21:31]

Done.

   DCHECK(!needs_tap_ending_event_);
 }
 
@@ -279,7 +282,7 @@ void TouchDispositionGestureFilter::CancelFlingIfNecessary() {
     return;
 
   SendGesture(
-      CreateGesture(ET_SCROLL_FLING_CANCEL, ending_event_motion_event_id_));
+      CreateGesture(ET_SCROLL_FLING_CANCEL, ending_event_motion_event_id_, 1));
   DCHECK(!needs_fling_ending_event_);
 }
 
@@ -288,7 +291,7 @@ void TouchDispositionGestureFilter::EndScrollIfNecessary() {
     return;
 
   SendGesture(
-      CreateGesture(ET_GESTURE_SCROLL_END, ending_event_motion_event_id_));
+      CreateGesture(ET_GESTURE_SCROLL_END, ending_event_motion_event_id_, 1));
   DCHECK(!needs_scroll_ending_event_);
 }