Release slotId of TouchEvent when USE_XI2_MT defined

ui/base/x/events_x.cc

 // Copyright (c) 2011 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.
 
 #include "ui/base/events.h"
 
 #include <X11/Xlib.h>
 #include <X11/extensions/XInput2.h>
 #include <string.h>
 
@@ skipping 341 matching lines @@
   XIDeviceEvent* xievent = static_cast<XIDeviceEvent*>(xev->xcookie.data);
   if (!factory->IsMultiTouchDevice(xievent->sourceid)) {
     // TODO(sad): Come up with a way to generate touch-ids for multi-touch
     // events when touch-events are generated from a single-touch device.
     return slot;
   }
 
 #if defined(USE_XI2_MT)
   float tracking_id;
   if (!factory->ExtractTouchParam(
-         *xev, ui::TouchFactory::TP_TRACKING_ID, &tracking_id))
+         *xev, ui::TouchFactory::TP_TRACKING_ID, &tracking_id)) {
     LOG(ERROR) << "Could not get the slot ID for the event. Using 0.";
-  else
+  } else {
     slot = factory->GetSlotForTrackingID(tracking_id);
+    ui::EventType type = ui::EventTypeFromNative(xev);
+    if (type == ui::ET_TOUCH_CANCELLED ||
+        type == ui::ET_TOUCH_RELEASED) {
+      factory->ReleaseSlotForTrackingID(tracking_id);
+    }
+  }
 #else
   if (!factory->ExtractTouchParam(
          *xev, ui::TouchFactory::TP_SLOT_ID, &slot))
     LOG(ERROR) << "Could not get the slot ID for the event. Using 0.";
 #endif
   return slot;
 }
 
 float GetTouchRadiusX(const base::NativeEvent& native_event) {
   return GetTouchParamFromXEvent(native_event,
@@ skipping 40 matching lines @@
   // Make sure we use atom from current xdisplay, which may
   // change during the test.
   noop->xclient.message_type = XInternAtom(
       base::MessagePumpX::GetDefaultXDisplay(),
       "noop", False);
 #endif
   return noop;
 }
 
 }  // namespace ui