Revert of Don't refcount tracking id -> slot id mapping.

ui/events/devices/x11/touch_factory_x11.cc

Index: ui/events/devices/x11/touch_factory_x11.cc
diff --git a/ui/events/devices/x11/touch_factory_x11.cc b/ui/events/devices/x11/touch_factory_x11.cc
index 929c5959b109416334cf0ef74b004a255566ff05..1dce5048d6bff599e5ff41b83035b0885c2a4949 100644
--- a/ui/events/devices/x11/touch_factory_x11.cc
+++ b/ui/events/devices/x11/touch_factory_x11.cc
@@ -250,8 +250,14 @@
   return id_generator_.GetGeneratedID(tracking_id);
 }
 
+void TouchFactory::AcquireSlotForTrackingID(uint32 tracking_id) {
+  tracking_id_refcounts_[tracking_id]++;
+}
+
 void TouchFactory::ReleaseSlotForTrackingID(uint32 tracking_id) {
-  id_generator_.ReleaseNumber(tracking_id);
+  tracking_id_refcounts_[tracking_id]--;
+  if (tracking_id_refcounts_[tracking_id] == 0)
+    id_generator_.ReleaseNumber(tracking_id);
 }
 
 bool TouchFactory::IsTouchDevicePresent() {
@@ -264,6 +270,7 @@
   touch_events_disabled_ = false;
   touch_device_list_.clear();
   touchscreen_ids_.clear();
+  tracking_id_refcounts_.clear();
   id_generator_.ResetForTest();
 }