DevTools: [JsDocValidator] Refactor JsDoc annotation checkers

- Migrate to a uniform JS context-tracking mechanism
- Add tests

R=aandrey, eustas, sergeyv, vsevik
NOTRY=true

Review URL: https://codereview.chromium.org/137553005

git-svn-id: svn://svn.chromium.org/blink/trunk@166124 bbb929c8-8fbe-4397-9dbb-9b2b20218538