DevTools: Fix InjectedScriptSource.js compilation after r184583

TBR=aandrey
NOTRY=true

Review URL: https://codereview.chromium.org/689633006

git-svn-id: svn://svn.chromium.org/blink/trunk@184627 bbb929c8-8fbe-4397-9dbb-9b2b20218538