When --mpd is true, run _mpd variants first, then non-mpd.

When --mpd is true, run _mpd variants first, then non-mpd.

This makes it easier to benchmark _mpd variants in a profiler.

E.g.,

<profiler> out/Release/nanobench --images --config 8888 --loops -1 --match sp_desk_nytimes

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/c751ecb3681072fda53dd3cebeb2eb41fc73b314

[mtklein_C, 2015-06-15 15:49:17]

mtklein@chromium.org changed reviewers:
+ herb@google.com

[mtklein_C, 2015-06-15 15:49:22]

The CQ bit was checked by mtklein@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-06-15 15:49:30]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1184673006/1

[commit-bot: I haz the power, 2015-06-15 15:54:13]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-06-15 15:54:14]

Dry run: This issue passed the CQ dry run.

[herb_g, 2015-06-15 15:55:26]

lgtm

[mtklein, 2015-06-15 15:55:57]

The CQ bit was checked by mtklein@google.com

[commit-bot: I haz the power, 2015-06-15 15:56:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1184673006/1

[commit-bot: I haz the power, 2015-06-15 15:56:40]

Committed patchset #1 (id:1) as
https://skia.googlesource.com/skia/+/c751ecb3681072fda53dd3cebeb2eb41fc73b314