Remove CreatePlatformFile from file_util_proxy

Remove CreatePlatformFile from file_util_proxy

Most of file_util_proxy is going to be deleted soon (users have to migrate to
FileProxy) so this CL is quite superficial. It is intended to remove the last
uses of CreatePlatformFile so that the method can be removed and no new code
can ignore base::File.

BUG=322664
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=262781

[rvargas (doing something else), 2014-04-07 23:27:51]

PTAL

[willchan no longer on Chromium, 2014-04-08 17:45:27]

lgtm

[rvargas (doing something else), 2014-04-08 23:09:47]

The CQ bit was checked by rvargas@chromium.org

[commit-bot: I haz the power, 2014-04-08 23:11:07]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rvargas@chromium.org/227433006/1

[commit-bot: I haz the power, 2014-04-08 23:44:03]

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

[commit-bot: I haz the power, 2014-04-08 23:44:03]

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

[rvargas (doing something else), 2014-04-09 15:31:35]

The CQ bit was checked by rvargas@chromium.org

[commit-bot: I haz the power, 2014-04-09 15:31:44]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/rvargas@chromium.org/227433006/1

[commit-bot: I haz the power, 2014-04-09 19:58:59]

Change committed as 262781