Disable power.top_25 perf test on Mac

Disable power.top_25 on Mac

This test has been flaky in the last 2 weeks on Mac bots.
(Adding NOTRY as everything is currently red on the perf waterfall)

BUG=489214
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

Committed: https://crrev.com/7116b1bd90afd5df23a3d09f4315a97a13b583ae
Cr-Commit-Position: refs/heads/master@{#330346}

[Primiano Tucci (use gerrit), 2015-05-18 10:39:39]

primiano@chromium.org changed reviewers:
+ andresantoso@chromium.org, skyostil@chromium.org

[Sami, 2015-05-18 10:49:24]

Thanks, lgtm.

[Primiano Tucci (use gerrit), 2015-05-18 10:55:22]

The CQ bit was checked by primiano@chromium.org

[commit-bot: I haz the power, 2015-05-18 10:55:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1129833005/40001

[commit-bot: I haz the power, 2015-05-18 10:59:31]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-05-18 11:34:26]

Patchset 3 (id:??) landed as
https://crrev.com/7116b1bd90afd5df23a3d09f4315a97a13b583ae
Cr-Commit-Position: refs/heads/master@{#330346}