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

ui/events/devices/x11/touch_factory_x11.h

Index: ui/events/devices/x11/touch_factory_x11.h
diff --git a/ui/events/devices/x11/touch_factory_x11.h b/ui/events/devices/x11/touch_factory_x11.h
index 775b496629ada69fb469d02ba10c62287e18a69b..cbec35f860b51ad2e6221bab0aea00833e86a2d6 100644
--- a/ui/events/devices/x11/touch_factory_x11.h
+++ b/ui/events/devices/x11/touch_factory_x11.h
@@ -67,6 +67,10 @@
   // isn't one already, allocates a new slot ID and sets up the mapping.
   int GetSlotForTrackingID(uint32 tracking_id);
 
+  // Increases the number of times |ReleaseSlotForTrackingID| needs to be called
+  // on a given tracking id before it will actually be released.
+  void AcquireSlotForTrackingID(uint32 tracking_id);
+
   // Releases the slot ID mapping to tracking ID.
   void ReleaseSlotForTrackingID(uint32 tracking_id);
 
@@ -126,6 +130,10 @@
   // Touch screen <vid, pid>s.
   std::set<std::pair<int, int> > touchscreen_ids_;
 
+  // Maps from a tracking id to the number of times |ReleaseSlotForTrackingID|
+  // must be called before the tracking id is released.
+  std::map<uint32, int> tracking_id_refcounts_;
+
   // Device ID of the virtual core keyboard.
   int virtual_core_keyboard_device_;