Refcount touch tracking ids to prevent freeing them too early.

ui/events/x/touch_factory_x11.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_EVENTS_X_TOUCH_FACTORY_X11_H_
 #define UI_EVENTS_X_TOUCH_FACTORY_X11_H_
 
 #include <bitset>
 #include <map>
 #include <set>
@@ skipping 50 matching lines @@
 
   // Tries to find an existing slot ID mapping to tracking ID. Returns true
   // if the slot is found and it is saved in |slot|, false if no such slot
   // can be found.
   bool QuerySlotForTrackingID(uint32 tracking_id, int* slot);
 
   // Tries to find an existing slot ID mapping to tracking ID. If there
   // 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);
 
   // Whether any touch device is currently present and enabled.
   bool IsTouchDevicePresent();
 
   // Pairs of <vendor id, product id> of external touch screens.
   const std::set<std::pair<int, int> >& GetTouchscreenIds() const {
     return touchscreen_ids_;
   }
@@ skipping 42 matching lines @@
   // The list of touch devices. For testing/debugging purposes, a single-pointer
   // device (mouse or touch screen without sufficient X/driver support for MT)
   // can sometimes be treated as a touch device. The key in the map represents
   // the device id, and the value represents if the device is multi-touch
   // capable.
   std::map<int, bool> touch_device_list_;
 
   // 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
   // digitizer.
   int max_touch_points_;
 
   SequentialIDGenerator id_generator_;
 
   DISALLOW_COPY_AND_ASSIGN(TouchFactory);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_X_TOUCH_FACTORY_X11_H_