Allow MakeCriticalClosure to enclose closures with non-void return types.

Allow MakeCriticalClosure to enclose closures with non-void return types.

This is required in order to allow ImportantFileWriter::WriteFileAtomically() to report its bool result to the calling thread via PostTaskAndReplyWithResult() in https://codereview.chromium.org/257003007/

BUG=365769
R=stuartmorgan@chromium.org, thakis@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=269238

[gab, 2014-05-07 23:39:49]

Nico/Stuart PTAL, split off from https://codereview.chromium.org/257003007/ as
requested.

[Nico, 2014-05-07 23:59:23]

this lgtm if Stuart likes it.

[gab, 2014-05-08 02:49:45]

On 2014/05/07 23:59:23, Nico wrote:
> this lgtm if Stuart likes it.

Thanks, Stuart please CQ if this LGTYs.

[stuartmorgan, 2014-05-08 16:55:28]

The inlining due to the templates makes me sad, since this makes the header
really confusing, but LGTM since it's apparently what we do.

[gab, 2014-05-08 16:56:12]

The CQ bit was checked by gab@chromium.org

[commit-bot: I haz the power, 2014-05-08 17:00:42]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/gab@chromium.org/274773003/1

[commit-bot: I haz the power, 2014-05-08 21:05:50]

FYI, CQ is re-trying this CL (attempt #1).
Please consider checking whether the failures are real,
and report flakes to chrome-troopers@google.com.
The failing builders are:
  win_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_rel/buil...)

[gab, 2014-05-09 11:58:11]

Committed patchset #1 manually as r269238 (presubmit successful).