This functionality causes a race during tests that may cause flaky
failures. Specifically, in the case of
ChangeIT#abandonAndRestoreAllowedWithPermission:
1. ACL grant on the main thread (A) modifies refs/meta/config, which
triggers ReindexAfterRefUpdate, which kicks off a background task
(thread B) to search for and reindex affected changes.
2. B reads change from primary storage, observes that it is open, and
constructs a document.
3. A abandons the change, saves the result in primary storage.
4. A indexes the change, deleting it from the open index and adding it
to the closed index.
5. B indexes the document it constructed in (2), adding it to the open
index.
6. A attempts to look up the change, finds it in both the open and
closed indexes, and explodes.
Turning off auto-reindexing causes tests to pass.
The race still exists in running servers, although in practice the
inconsistent cases are fleeting and the index should usually end up in a
consistent state. More details and reflections are in the bug.
Bug: Issue 5944
Change-Id: Ifca5a1065852db38a562755b652fad3de3672816
3396e57b52