DevTools: Prefactoring for strict nullability operators in the frontend JsDoc

R=aandrey, caseq, vsevik
BUG=324831

Review URL: https://codereview.chromium.org/106623002

git-svn-id: svn://svn.chromium.org/blink/trunk@163340 bbb929c8-8fbe-4397-9dbb-9b2b20218538