Migrate process_dice_header_delegate_impl_unittest.cc to IdentityTestEnvironment

After successfully migrating the ProcessDiceHeaderDelegateImpl we can
complete the job by also migrating the unit test. Several fake objects
were removed in favour of IdentityTestEnvironment which also provides
an IdentityManager.

Bug: 890791
Change-Id: Ie689268b0b9e2569a4cce5c4abe645d3daa82c7e
Reviewed-on: https://chromium-review.googlesource.com/c/1282743
Reviewed-by: Colin Blundell <blundell@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Commit-Queue: Sergio Villar <svillar@igalia.com>
Cr-Commit-Position: refs/heads/master@{#599985}
1 file changed