[fsp] Add an initial AsyncFileUtil.

[fsp] 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.

TEST=unit_test: FileSystemProviderAsyncFileUtilTest*
BUG=248427
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=264462

[mtomasz, 2014-04-16 09:17:05]

@kinaba: PTAL. Thanks!

[kinaba, 2014-04-17 05:27:07]

lgtm

[mtomasz, 2014-04-17 06:21:20]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2014-04-17 06:21:28]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/mtomasz@chromium.org/236303017/40001

[commit-bot: I haz the power, 2014-04-17 07:48:37]

Change committed as 264462

[dconnelly, 2014-04-17 12:11:31]

A revert of this CL has been created in
https://codereview.chromium.org/240483008/ by dconnelly@chromium.org.

The reason for reverting is: Broke Linux Chromium OS Tests -- looks like the new
tests aren't working properly there.

Failing build:
http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%2....

[mtomasz, 2014-04-18 01:23:38]

On 2014/04/17 12:11:31, dconnelly wrote:
> A revert of this CL has been created in
> https://codereview.chromium.org/240483008/ by mailto:dconnelly@chromium.org.
> 
> The reason for reverting is: Broke Linux Chromium OS Tests -- looks like the
new
> tests aren't working properly there.
> 
> Failing build:
>
http://build.chromium.org/p/chromium.chromiumos/builders/Linux%20ChromiumOS%2....

@kinaba: I've just fixed the tests. The root cause for the test failure on Debug
was that I was creating a non-cracked testing URL with a kFileSystemTypeProvided
as a top level type, which is incorrect. Instead, a cracked file system url
should be crated with kFileSystemTypeExternal as url.mount_type() and
kFileSystemTypeProvided as url.type(). However, to create a cracked URL, we need
the mount point. The latest patch introduces a ScopedExternalMountPoint to
create a testing mount point valid during each test case. PTAL. Thanks.

[kinaba, 2014-04-18 03:48:33]

lgtm