Test time complexity for page with large inlined script.

Relies on on async magnitude-perf API:
https://codereview.chromium.org/544453004/

Tests fix:
https://codereview.chromium.org/494993002/

BUG=410790

Review URL: https://codereview.chromium.org/500363002

git-svn-id: svn://svn.chromium.org/blink/trunk@181650 bbb929c8-8fbe-4397-9dbb-9b2b20218538