Add missing copyright header for NavigatorOnLine.idl

I forgot to include the copyright header for NavigatorOnLine.idl in r156392.

TBR=haraken

Review URL: https://codereview.chromium.org/22929010

git-svn-id: svn://svn.chromium.org/blink/trunk@156393 bbb929c8-8fbe-4397-9dbb-9b2b20218538