Move test cases of the navigator content utils to own directory

Navigator content utils test will be added further. It would be good
to have own test directory.

BUG=N/A

Review URL: https://codereview.chromium.org/144313006

git-svn-id: svn://svn.chromium.org/blink/trunk@165595 bbb929c8-8fbe-4397-9dbb-9b2b20218538