Refcount touch tracking ids to prevent freeing them too early.

ui/events/x/events_x.cc

Index: ui/events/x/events_x.cc
diff --git a/ui/events/x/events_x.cc b/ui/events/x/events_x.cc
index 03b7e28d8de9704453e90d7dde5a6e126667863b..d463221eaa58a8b4b772b17e301a3370b6ec3f00 100644
--- a/ui/events/x/events_x.cc
+++ b/ui/events/x/events_x.cc
@@ -644,6 +644,18 @@ void ReleaseCopiedNativeEvent(const base::NativeEvent& event) {
   delete event;
 }
 
+void IncrementTouchIdRefCount(const base::NativeEvent& xev) {
+  ui::DeviceDataManagerX11* manager = ui::DeviceDataManagerX11::GetInstance();
+  double tracking_id;
+  if (!manager->GetEventData(
+          *xev, ui::DeviceDataManagerX11::DT_TOUCH_TRACKING_ID, &tracking_id)) {
+    return;
+  }
+
+  ui::TouchFactory* factory = ui::TouchFactory::GetInstance();
+  factory->AcquireSlotForTrackingID(tracking_id);

[sadrul, 2014/07/22 16:49:16]

Should we do this automagically from GetTouchId() when event-type is
TOUCH_PRESSED? It feels bad to add yet-another X11-only event_utils method that
no other platforms need to implement, but it also feels bad for GetTouchId() to
have a side-effect like this. WDYT?

[tdresser, 2014/07/22 20:17:08]

As we just discussed in person, I think there's a lot of value in having the
calls to |IncrementTouchIdRefCount| and |ClearTouchIdIfReleased| in the
constructor and destructor respectively, as it makes it obvious that they match
up.

I'm inclined to go with the current solution.

+}
+
 void ClearTouchIdIfReleased(const base::NativeEvent& xev) {
   ui::EventType type = ui::EventTypeFromNative(xev);
   if (type == ui::ET_TOUCH_CANCELLED ||