Distinquish TestWithIsolateAndZone from TestWithZone

Distinquish TestWithIsolateAndZone from TestWithZone

Allows unit tests that just need a zone and no isolate to avoid the overhead of
creating one.

R=mstarzinger@chromium.org
LOG=N

Review URL: https://codereview.chromium.org/871843004

Cr-Commit-Position: refs/heads/master@{#26256}