Release slotId of TouchEvent when USE_XI2_MT defined

ui/base/x/events_x.cc

Index: ui/base/x/events_x.cc
diff --git a/ui/base/x/events_x.cc b/ui/base/x/events_x.cc
index 59767293684217eb80346e35225ec65c75b3b887..4f2db853d7cb08892f4f8cb9a49e6dc114fc288a 100644
--- a/ui/base/x/events_x.cc
+++ b/ui/base/x/events_x.cc
@@ -359,10 +359,16 @@ int GetTouchId(const base::NativeEvent& xev) {
 #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))