worker: Use standard task-runners to run notification image loader callbacks.

notifications: Use standard task-runners to run image loader callbacks.

Instead of using the id of the worker-thread to keep track of the thread to
run the image-loader callbacks on, use the task-runner of the thread instead.

BUG=none
R=mkwst@chromium.org

Committed: https://chromium.googlesource.com/chromium/src/+/609de4573984d34743ce3e237855469a946a27d4

[sadrul, 2015-02-03 23:41:36]

sadrul@chromium.org changed reviewers:
+ mkwst@chromium.org

[Mike West, 2015-02-04 12:17:32]

It's not clear to me what effects this change will have. Why should we use the
one and not the other?

[Mike West, 2015-02-04 12:17:59]

(Also, the bots seem to pretty consistently not like this change :) )

[sadrul, 2015-02-04 14:17:23]

On 2015/02/04 12:17:32, Mike West wrote:
> It's not clear to me what effects this change will have. Why should we use the
> one and not the other?

This change should not have any effects. Using WorkerTaskRunner to PostTask
essentially does the same thing, but in a roundabout way. Using base::TaskRunner
interface to do this is more consistent with how tasks are sent across threads
in other places. (another recent change to do the same changes for fileapi
callbacks: https://codereview.chromium.org/893233002/)

> (Also, the bots seem to pretty consistently not like this change :) )

Whoops. I had a typo in there. Sorry! Fixed now. The trybots are happier.

[sadrul, 2015-02-06 15:50:19]

ping

[Mike West, 2015-02-06 17:07:00]

LGTM.

[commit-bot: I haz the power, 2015-02-06 21:24:56]

Patchset 3 (id:??) landed as
https://crrev.com/609de4573984d34743ce3e237855469a946a27d4
Cr-Commit-Position: refs/heads/master@{#315109}

[sadrul, 2015-02-06 21:25:08]

Committed patchset #3 (id:40001) manually as
609de4573984d34743ce3e237855469a946a27d4 (presubmit successful).