Update license header in generated files

Per:
http://www.chromium.org/blink/coding-style#TOC-License

Review URL: https://codereview.chromium.org/54673008

git-svn-id: svn://svn.chromium.org/blink/trunk@161136 bbb929c8-8fbe-4397-9dbb-9b2b20218538