Remove [LegacyTreatAsPartialInterface] from NavigatorID and NavigatorOnLine

Also allows us to delete NavigatorBase class.

R=haraken
BUG=360435

Review URL: https://codereview.chromium.org/227603002

git-svn-id: svn://svn.chromium.org/blink/trunk@171014 bbb929c8-8fbe-4397-9dbb-9b2b20218538