Add ShellNetworkDelegate so content_shell can use cookies (again)

BUG=none
TEST=try to log in to some site using content_shell

Review URL: https://chromiumcodereview.appspot.com/9701023

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@129589 0039d316-1c4b-4281-b951-d872f2087c98