[fsp] Convert base::File::Error to string.

[fsp] Convert base::File::Error to string.

This patch adds a utility function which converts a base::File::Error code
to a human readable form. It will be used for logging request errors in the
File System Provider API.

TEST=Not used yet.
BUG=376095
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=273779

[mtomasz, 2014-05-29 06:29:32]

@rvargas: PTAL. Thanks.

[rvargas (doing something else), 2014-05-29 19:07:27]

LGTM after the nit.

https://codereview.chromium.org/308613002/diff/20001/base/files/file.h
File base/files/file.h (right):

https://codereview.chromium.org/308613002/diff/20001/base/files/file.h#newcode8
base/files/file.h:8: #include <string>
nit: This should go after <windows> and <sys/stat.h>

[mtomasz, 2014-05-30 00:25:41]

The CQ bit was checked by mtomasz@chromium.org

[mtomasz, 2014-05-30 00:25:55]

https://codereview.chromium.org/308613002/diff/20001/base/files/file.h
File base/files/file.h (right):

https://codereview.chromium.org/308613002/diff/20001/base/files/file.h#newcode8
base/files/file.h:8: #include <string>
On 2014/05/29 19:07:27, rvargas wrote:
> nit: This should go after <windows> and <sys/stat.h>

Done.

[commit-bot: I haz the power, 2014-05-30 00:27:23]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mtomasz@chromium.org/308613002/40001

[commit-bot: I haz the power, 2014-05-30 05:07:47]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  win_chromium_x64_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/win_chromium_x64_rel/...)

[commit-bot: I haz the power, 2014-05-30 10:07:32]

Change committed as 273779