App-to-Web: Use userContext when getting DomainVerificationManager.

Since DVM uses context.userId in its implementation, we need to supply
the right user context when retriving DVM so it saves to the correct
user.

Bug: 399181562
Test: Manual. on HSUM devices, choosing the dialog option -> reopen, see
option sticks
Flag: EXEMPT bugfix

Change-Id: I83cb0d93a81bdb282e16bcdc9c472855eea6e83d