Remove support for AllowBackgroundModeFromRenderer group in BackgroundRendererProcesses experiment.

Remove support for AllowBackgroundModeFromRenderer group in BackgroundRendererProcesses experiment.

This group was only intended to be ran on early channels to show that we are tracking the right stats and ensure that the latest background mode experiment isn't bringing back the regressions that mode had previously brought (see issue 381820 and issue 398103).

The analysis is complete and support for it in the client is no longer required (already ramped down server-side).

(this is essentially a partial revert of https://codereview.chromium.org/926663002)

BUG=459600
Committed: https://crrev.com/e194b5d49e4c0bc231e73acb4290e3d5a23fd97f
Cr-Commit-Position: refs/heads/master@{#325445}

[gab, 2015-04-16 13:10:55]

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

[gab, 2015-04-16 13:11:52]

gab@chromium.org changed reviewers:
+ jam@chromium.org

[gab, 2015-04-16 13:11:52]

John, PTAL.

Thanks,
Gab

[commit-bot: I haz the power, 2015-04-16 13:12:16]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1089873002/1

[commit-bot: I haz the power, 2015-04-16 13:22:19]

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

[commit-bot: I haz the power, 2015-04-16 13:22:20]

Dry run: Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromium_presub...)

[jam, 2015-04-16 14:48:50]

lgtm

[gab, 2015-04-16 15:06:02]

The CQ bit was checked by gab@chromium.org

[commit-bot: I haz the power, 2015-04-16 15:06:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1089873002/1

[commit-bot: I haz the power, 2015-04-16 15:09:44]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-16 15:11:12]

Patchset 1 (id:??) landed as
https://crrev.com/e194b5d49e4c0bc231e73acb4290e3d5a23fd97f
Cr-Commit-Position: refs/heads/master@{#325445}