Final touches on enums as mojom types.

1. Referencing enums from another struct now works.
2. Referencing enum constants now works in all cases.

BUG=320090

Review URL: https://codereview.chromium.org/180703003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254270 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254270
Cleanup ServiceWorkerStorage class (and registration flow)

Fixing some TODOs in ServiceWorkerStorage:
- Implement async StoreRegistration() and DeleteRegistration() to deprecate temporary internal synchronous methods
- Move registration creation & shutdown code out of ServiceWorkerStorage
- Add generic ERROR_NOT_FOUND status code and cleanup Found*() methods to return a single status code

Also made some refactor & cleanups in ServiceWorkerRegisterJob so that
new async ServiceWorkerStorage methods can fit in.

BUG=none

Review URL: https://codereview.chromium.org/184593002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254271 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254271