Removes waiter member from BackgroundOfflinerTask to make it easier to reason about thread safety

Removes waiter member from BackgroundOfflinerTask to make it easier to reason about thread safety
(eg, don't have to worry about two concurrent calls).

BUG=612325
Committed: https://crrev.com/3b44616bcf69700ca97c8ca219ac3414a8cc1254
Cr-Commit-Position: refs/heads/master@{#400298}

[dougarnett, 2016-06-16 22:04:34]

dougarnett@chromium.org changed reviewers:
+ fgorski@chromium.org, petewil@chromium.org

[Pete Williamson, 2016-06-16 22:06:48]

lgtm

[dougarnett, 2016-06-16 22:53:17]

The CQ bit was checked by dougarnett@chromium.org

[commit-bot: I haz the power, 2016-06-16 22:54:13]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/2071073002/1

[commit-bot: I haz the power, 2016-06-16 23:39:03]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-06-16 23:41:02]

Description was changed from

==========
Removes waiter member from BackgroundOfflinerTask to make it easier to reason
about thread safety
(eg, don't have to worry about two concurrent calls).

BUG=612325
==========

to

==========
Removes waiter member from BackgroundOfflinerTask to make it easier to reason
about thread safety
(eg, don't have to worry about two concurrent calls).

BUG=612325

Committed: https://crrev.com/3b44616bcf69700ca97c8ca219ac3414a8cc1254
Cr-Commit-Position: refs/heads/master@{#400298}
==========

[commit-bot: I haz the power, 2016-06-16 23:41:03]

Patchset 1 (id:??) landed as
https://crrev.com/3b44616bcf69700ca97c8ca219ac3414a8cc1254
Cr-Commit-Position: refs/heads/master@{#400298}