Part 2 of fix. Denies access to password manager for sandboxed iframes with allow-same-origin not set.

      BUG=42980
TEST=None

Review URL: http://codereview.chromium.org/2110008

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@47889 0039d316-1c4b-4281-b951-d872f2087c98