Refcount touch tracking ids to prevent freeing them too early.

ui/events/x/touch_factory_x11.h

Index: ui/events/x/touch_factory_x11.h
diff --git a/ui/events/x/touch_factory_x11.h b/ui/events/x/touch_factory_x11.h
index 4d8a989fd8f87fe20a68a3c89e6a990ad5c6abaf..051f3de0bc04057cf2e58a89faad542fd7785623 100644
--- a/ui/events/x/touch_factory_x11.h
+++ b/ui/events/x/touch_factory_x11.h
@@ -68,6 +68,10 @@ class EVENTS_BASE_EXPORT TouchFactory {
   // 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);
 
@@ -130,6 +134,10 @@ class EVENTS_BASE_EXPORT TouchFactory {
   // 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_;
+
   // Maximum simultaneous touch points supported by device. In the case of
   // devices with multiple digitizers (e.g. multiple touchscreens), the value
   // is the maximum of the set of maximum supported contacts by each individual