GitLab

This CL add two assertions that abstracts the checks for JavaScript
traits.

 - should().ownProperty()
 - should().inheritFrom()

BUG=702708
TEST=webaudio/unit-tests/audit.html

Review-Url: https://codereview.chromium.org/2805773002
Cr-Commit-Position: refs/heads/master@{#462970}