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

ui/events/event.h

Index: ui/events/event.h
diff --git a/ui/events/event.h b/ui/events/event.h
index 427a731c0a203a44500cdbf1eadb34c60be0feb3..d1fbab5c5d06d499e276f03f4ab2050c145b7c2e 100644
--- a/ui/events/event.h
+++ b/ui/events/event.h
@@ -224,9 +224,6 @@ class EVENTS_EXPORT Event {
   Event(const base::NativeEvent& native_event, EventType type, int flags);
   Event(const Event& copy);
   void SetType(EventType type);
-  void set_delete_native_event(bool delete_native_event) {
-    delete_native_event_ = delete_native_event;
-  }
   void set_cancelable(bool cancelable) { cancelable_ = cancelable; }
 
   void set_time_stamp(const base::TimeDelta& time_stamp) {
@@ -492,8 +489,8 @@ class EVENTS_EXPORT TouchEvent : public LocatedEvent {
         radius_x_(model.radius_x_),
         radius_y_(model.radius_y_),
         rotation_angle_(model.rotation_angle_),
-        force_(model.force_) {
-  }
+        force_(model.force_),
+        should_remove_native_touch_id_mapping_(false) {}
 
   TouchEvent(EventType type,
              const gfx::PointF& location,
@@ -522,6 +519,12 @@ class EVENTS_EXPORT TouchEvent : public LocatedEvent {
   void set_radius_x(const float r) { radius_x_ = r; }
   void set_radius_y(const float r) { radius_y_ = r; }
 
+  void set_should_remove_native_touch_id_mapping(
+      bool should_remove_native_touch_id_mapping) {
+    should_remove_native_touch_id_mapping_ =
+        should_remove_native_touch_id_mapping;
+  }
+
   // Overridden from LocatedEvent.
   void UpdateForRootTransform(
       const gfx::Transform& inverted_root_transform) override;
@@ -554,6 +557,13 @@ class EVENTS_EXPORT TouchEvent : public LocatedEvent {
 
   // Force (pressure) of the touch. Normalized to be [0, 1]. Default to be 0.0.
   float force_;
+
+  // True if this event should remove the mapping between the native
+  // event id and the chromium touch id. This should only be the case
+  // for release and cancel events where the associated touch press
+  // event created a mapping between the native id and the chromium
+  // touch id.
+  bool should_remove_native_touch_id_mapping_;
 };
 
 // An interface that individual platforms can use to store additional data on