[fsp] [recommit] Add an initial AsyncFileUtil.

[fsp] [recommit] Add an initial AsyncFileUtil.

This patch adds the AsyncFileUtil implementation for the file system provider.
It does not communicate with the file system provider service yet.

Currently, for not supported operations SECURITY error is returned. For
allowed, but not implemented operations, it is NOT_FOUND error.

Unit tests are quite trivial at this stage, but they will grow once more
operations are implemented.

This patch has been previously committed and reverted due to test failures.
See: https://codereview.chromium.org/236303017/

TEST=unit_test: FileSystemProviderAsyncFileUtilTest*
BUG=248427
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=264778

[mtomasz, 2014-04-18 03:54:06]

@kinaba: This identical to https://codereview.chromium.org/236303017/, but
required to recommit via CQ. PTAL. Thanks.

[kinaba, 2014-04-18 03:54:44]

lgtm

[mtomasz, 2014-04-18 03:55:41]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2014-04-18 03:55:55]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mtomasz@chromium.org/242493002/1

[commit-bot: I haz the power, 2014-04-18 05:40:00]

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

[commit-bot: I haz the power, 2014-04-18 05:40:01]

Try jobs failed on following builders:
  tryserver.chromium on win_chromium_rel

[mtomasz, 2014-04-18 05:41:13]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2014-04-18 05:41:32]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mtomasz@chromium.org/242493002/1

[commit-bot: I haz the power, 2014-04-18 12:29:47]

Change committed as 264778