1. Returns icon of the incognito guy to the tab header.
2. Sets NTP as homepage for the guest mode.
3. Adds the missing separator between the options.

BUG=chromium-os:9534
TEST=manual

Review URL: http://codereview.chromium.org/5314002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@67125 0039d316-1c4b-4281-b951-d872f2087c98