[Variations] Read the policy from profile prefs if on Android

BUG=342839
TEST=Manually tested with a User Policy file running on an Android build.

Review URL: https://codereview.chromium.org/136003008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@250859 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 250859