Thread IO safety: annotate file_util, and block IO thread from doing IO

- Mark functions in file_util_posix as requiring permission to perform
  disk actions.
- Mark the IO thread as disallowed from performing disk actions.
- Temporarily work around the protections in places where we currently
  have bugs.

BUG=59847,59849,60207,60211,60394
TEST=no dchecks in debug builds

Review URL: http://codereview.chromium.org/3872002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@63636 0039d316-1c4b-4281-b951-d872f2087c98
14 files changed