Inline sign in flow with gaia auth extension

Design doc at https://docs.google.com/a/google.com/document/d/1L0gcqZEZ0lWL0PgqO6uPyecuxJdTvzZpps2zRly_wTg/edit#heading=h.5cwdwtkutcuo

BUG=302037

Review URL: https://codereview.chromium.org/25347002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226569 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226569
Reapply "ChildProcessSecurityPolicy: Rationalize PlatformFileFlags used."

See https://codereview.chromium.org/24631002/

Patchset 1 is the above CL as-it-was. Unfortunately, it adds some new static initializers, which can't go into tree.

Solution is to just remove the definitions from file_permission_policy and inline them into child_process_security_policy_impl. They aren't referenced anywhere in webkit anyways.

TBR=kinuko
BUG=262142, 263150

Review URL: https://codereview.chromium.org/25628002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@226570 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 226570