permissions: rework tests for requesting

This CL does several things:
(1) The lack of using a variable inside the inner request meant the
request test was just testing setPermisison. Fix the test by making it
use promises and make the error message more descriptive as well.
(2) Fix some broken comments.

BUG=(none)

Review URL: https://codereview.chromium.org/1352863002

Cr-Commit-Position: refs/heads/master@{#350532}
4 files changed