Mark inspector/layers/layer-canvas-log.html "Failure" on Mac

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#master=ChromiumWebkit&tests=inspector/layers/layer-canvas-log.html

BUG=430557
TBR=senorblanco@chromium.org, caseq@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/727663002

git-svn-id: svn://svn.chromium.org/blink/trunk@185339 bbb929c8-8fbe-4397-9dbb-9b2b20218538