SpeechPackDownloadController constructor Null safety

1. irte_engine
2. speech_pack_download_controller
3. SpeechPackDownloadController
4. SpeechPackDownloadController constructor

SpeechPackDownloadController class

1. Constructors
2. SpeechPackDownloadController
3. Properties
4. downloadProgress
5. hashCode
6. hasListeners
7. initialized
8. isClosed
9. listeners
10. onDelete
11. onStart
12. runtimeType
13. Methods
14. $configureLifeCycle
15. addListener
16. addListenerId
17. dispose
18. disposeId
19. download
20. noSuchMethod
21. notifyChildrens
22. onClose
23. onInit
24. onReady
25. refresh
26. refreshGroup
27. removeListener
28. removeListenerId
29. stopCurrentDownload
30. toString
31. update
32. updateProgress
33. Operators
34. operator ==
35. Static properties
36. instance