Speculative Layout Test fix for inspector/sources/debugger/promise-tracker.html

BUG=414163
TBR=loislo, amikhaylova@google.com

Review URL: https://codereview.chromium.org/568363003

git-svn-id: svn://svn.chromium.org/blink/trunk@181968 bbb929c8-8fbe-4397-9dbb-9b2b20218538