Plugin Power Saver: Record PPS UMAs only for users with PPS enabled.

Plugin Power Saver: Record PPS UMAs only for users with PPS enabled.

Previously, we collected PPS UMAs across all users. We created a throttler and used it in a 'simulated' mode.

Now that real PPS users exist, collect UMAs only on actual PPS users. This is accomplished by only creating a throttler when PPS is enabled.

BUG=470731
Committed: https://crrev.com/db0458c20b2fd343ce4a5c86a6777795ae10479f
Cr-Commit-Position: refs/heads/master@{#322462}

[tommycli, 2015-03-26 00:20:58]

tommycli@chromium.org changed reviewers:
+ bauerb@chromium.org, piman@chromium.org, thestig@chromium.org

[tommycli, 2015-03-26 00:26:22]

piman, thestig, bauerb: PTAL

Not a big patch. Appreciate reviews.

[Bernhard Bauer, 2015-03-26 09:27:48]

lgtm

[Lei Zhang, 2015-03-26 18:26:18]

lgtm

[piman, 2015-03-26 20:21:38]

lgtm

[tommycli, 2015-03-26 20:28:15]

The CQ bit was checked by tommycli@chromium.org

[tommycli, 2015-03-26 20:28:27]

piman, thestig, bauerb: Thank you all for the quick reviews.

[commit-bot: I haz the power, 2015-03-26 20:28:48]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1024493004/20001

[commit-bot: I haz the power, 2015-03-26 20:38:59]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-03-26 20:39:31]

Patchset 2 (id:??) landed as
https://crrev.com/db0458c20b2fd343ce4a5c86a6777795ae10479f
Cr-Commit-Position: refs/heads/master@{#322462}