Revert of Allow POSIX callers to specify a new file's mode.

Revert of Allow POSIX callers to specify a new file's mode. (patchset #1 id:1 of https://codereview.chromium.org/689713006/)

Reason for revert:
This seems to have broken the Linux MSan test bot.

[ RUN      ] FileUtilTest.WriteFileWithMode
../../base/files/file_util_unittest.cc:2164: Failure
Value of: status.st_mode & 0777
  Actual: 384
Expected: mode
Which is: 420
[  FAILED  ] FileUtilTest.WriteFileWithMode (1 ms)

Original issue's description:
> Allow POSIX callers to specify a new file's mode.
>
> Retain the tight 0640 mode for most existing callers, but honor the user's
> umask for downloaded files.
>
> This is a re-land of https://codereview.chromium.org/639253004/.
>
> BUG=409416, 362887
> TBR=asanka,mdempsky,rvargas
>
> Committed: https://crrev.com/931e35070097af9837f79ff19f8668e45b92ed3a
> Cr-Commit-Position: refs/heads/master@{#302113}

TBR=palmer@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=409416, 362887
Committed: https://crrev.com/8db8e88e009aba7fd5448383df2a4645802d19af
Cr-Commit-Position: refs/heads/master@{#302143}

[csharp1, 2014-10-30 20:10:36]

Created Revert of Allow POSIX callers to specify a new file's mode.

[commit-bot: I haz the power, 2014-10-30 20:12:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/693493004/1

[commit-bot: I haz the power, 2014-10-30 20:13:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-10-30 20:14:52]

Patchset 1 (id:??) landed as
https://crrev.com/8db8e88e009aba7fd5448383df2a4645802d19af
Cr-Commit-Position: refs/heads/master@{#302143}