startTrackingPointer method
Implementation
@protected
void startTrackingPointer(int pointer, [Matrix4? transform]) {
GestureBinding.instance!.pointerRouter.addRoute(pointer, handleEvent, transform);
_trackedSecondPointers.add(pointer);
assert(!_secondEntries.containsValue(pointer));
_secondEntries[pointer] = _addPointerToArena(pointer);
}