DevTools: Don't stop debugger inside V8 internal scripts with empty stack trace.

R=yurys
TEST=inspector/sources/debugger/debugger-autocontinue-on-syntax-error.html, inspector/sources/debugger/debugger-step-into-v8-internals.html

Review URL: https://codereview.chromium.org/424813004

git-svn-id: svn://svn.chromium.org/blink/trunk@179137 bbb929c8-8fbe-4397-9dbb-9b2b20218538