onActivate property Null safety

1. Flutter
2. dart:html
3. ServiceWorkerGlobalScope
4. onActivate property

ServiceWorkerGlobalScope class

1. Properties
2. addressSpace
3. caches
4. clients
5. crypto
6. hashCode
7. indexedDB
8. isSecureContext
9. location
10. navigator
11. on
12. onActivate
13. onError
14. onFetch
15. onForeignfetch
16. onInstall
17. onMessage
18. origin
19. performance
20. registration
21. runtimeType
22. self
23. Methods
24. addEventListener
25. atob
26. btoa
27. dispatchEvent
28. fetch
29. importScripts
30. noSuchMethod
31. removeEventListener
32. skipWaiting
33. toString
34. Operators
35. operator ==
36. Static properties
37. instance
38. Constants
39. activateEvent
40. fetchEvent
41. foreignfetchEvent
42. installEvent
43. messageEvent