Disable blink_perf.canvas on the reference build
The benchmark is generating garbage values on the reference build,
leading to a failure when we try to compute the standard deviation of
the results.
BUG=520092
CQ_EXTRA_TRYBOTS=tryserver.chromium.perf:linux_perf_bisect;tryserver.chromium.perf:mac_perf_bisect;tryserver.chromium.perf:win_perf_bisect;tryserver.chromium.perf:android_nexus5_perf_bisect
Review URL: https://codereview.chromium.org/
1292063006
Cr-Commit-Position: refs/heads/master@{#343371}