Re-enable blink_perf.canvas on Windows 7

Re-enable blink_perf.canvas on Windows 7

Reason for re-enabling:
Relanding as the fix crrev.com/1308853003 rolled in.

Original issue's description being reverted:
> Disable blink_perf.canvas on Windows 7
>
> The test has been failing consistently on the Windows 7 Low-End bot.
> See http://build.chromium.org/p/chromium.perf/builders/Win%207%20Low-End%20Perf%20%282%29/builds/2593/steps/blink_perf.canvas/logs/stdio
>
> BUG=522972
> 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
>
> Committed: https://crrev.com/3cf6e609237cbde98522239d5d9016908a2a39f1
> Cr-Commit-Position: refs/heads/master@{#344531}

TBR=junov@chromium.org,sullivan@chromium.org
BUG=522972

Review URL: https://codereview.chromium.org/1309753004

Cr-Commit-Position: refs/heads/master@{#345043}