Use net::TestClosureCallback in SimpleCache tests.

Use net::TestClosureCallback in SimpleCache tests.

Reduces flakiness; improves test readability. Also introduces a
callback on SimpleIndexFile to signal completion of writing the index,
useful for deflaking cache serialization.

R=jkarlin@chromium.org
BUG=255775, 429672
Committed: https://crrev.com/f379a6efd4f9beb6cc49e7f4e00286dfc2717dcf
Cr-Commit-Position: refs/heads/master@{#302653}

[gavinp, 2014-11-03 23:05:37]

This is downstream of https://codereview.chromium.org/699693002/ , and it
further deflakes the tests by using the new TestClosure mechanism to track the
various steps in this index test rather than trusting run loops to finish at the
right stages.

[jkarlin, 2014-11-04 02:24:30]

lgtm

[gavinp, 2014-11-04 08:14:30]

The CQ bit was checked by gavinp@chromium.org

[commit-bot: I haz the power, 2014-11-04 08:16:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/699743002/60001

[commit-bot: I haz the power, 2014-11-04 08:20:59]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-11-04 08:21:00]

Try jobs failed on following builders:
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/77284)
  win_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu/builds/82255)
  win8_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)
  win_chromium_compile_dbg on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_comp...)
  win_chromium_rel_ng on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)
  win_chromium_x64_rel_ng on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[gavinp, 2014-11-04 16:04:57]

On 2014/11/04 08:21:00, I haz the power (commit-bot) wrote:
> Try jobs failed on following builders:
>   mac_gpu on tryserver.chromium.gpu
>
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/77284)
>   win_gpu on tryserver.chromium.gpu
>
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/win_gpu/builds/82255)
>   win8_chromium_rel on tryserver.chromium.win
>
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)
>   win_chromium_compile_dbg on tryserver.chromium.win
>
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_comp...)
>   win_chromium_rel_ng on tryserver.chromium.win
>
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)
>   win_chromium_x64_rel_ng on tryserver.chromium.win
>
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

Whoops: of course this can't land, it's downstream of
https://codereview.chromium.org/705433002/  :-)

[gavinp, 2014-11-04 18:40:49]

upstream has now landed. making a nonce upload and rerunning tests.

[gavinp, 2014-11-04 19:29:49]

The CQ bit was checked by gavinp@chromium.org

[commit-bot: I haz the power, 2014-11-04 19:32:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/699743002/80001

[commit-bot: I haz the power, 2014-11-04 20:21:04]

Committed patchset #5 (id:80001)

[commit-bot: I haz the power, 2014-11-04 20:22:01]

Patchset 5 (id:??) landed as
https://crrev.com/f379a6efd4f9beb6cc49e7f4e00286dfc2717dcf
Cr-Commit-Position: refs/heads/master@{#302653}