GitLab

Recently imported test
external/wpt/media-source/mediasource-avtracks.html is occasionally
failing instead of crashing on WebKit Mac 10.9, so expanding the
test expectation to accommodate.

BUG=626703
TBR=jochen@chromium.org

Review-Url: https://codereview.chromium.org/2856823002
Cr-Commit-Position: refs/heads/master@{#468573}