Teach check-webkit-style about C++11 override and final.

It previously only allowed trailing "const" and "OVERRIDE".
We now encourage use of the "override" and "final" keywords.
While here, also add the previously omitted (but deprecated) "FINAL" macro.

TEST=webkitpy.style.checkers.cpp_unittest

Review URL: https://codereview.chromium.org/606393002

git-svn-id: svn://svn.chromium.org/blink/trunk@182825 bbb929c8-8fbe-4397-9dbb-9b2b20218538