Disable blink_perf.canvas on Windows

This test is failing reliably on the Windows GPU bots.

BUG=488493
NOTRY=true
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/1145583002

Cr-Commit-Position: refs/heads/master@{#330126}

tools/perf/benchmarks/blink_perf.py

@@ -167,6 +167,7 @@ class BlinkPerfCSS(benchmark.Benchmark):
     return CreatePageSetFromPath(path, SKIPPED_FILE)
 
 
+@benchmark.Disabled('win')  # http://crbug.com/488493
 class BlinkPerfCanvas(benchmark.Benchmark):
   tag = 'canvas'
   test = _BlinkPerfMeasurement