DevTools: Extract JS module declarations from compile_frontend.py into js_modules

R=aandrey, eustas, vsevik
NOTRY=true

Review URL: https://codereview.chromium.org/119823003

git-svn-id: svn://svn.chromium.org/blink/trunk@164216 bbb929c8-8fbe-4397-9dbb-9b2b20218538