[Session restore] Add DontRestoreBackgroundTabs group to collect stats.

[Session restore] Add DontRestoreBackgroundTabs group to collect stats.

BUG=472772
Committed: https://crrev.com/1912f4a4c9126ed44b1d660cb4451be204738433
Cr-Commit-Position: refs/heads/master@{#329245}

[Georges Khalil, 2015-05-11 20:11:53]

georgesak@chromium.org changed reviewers:
+ sky@chromium.org

[Georges Khalil, 2015-05-11 20:11:53]

PTAL.

This adds the lazy mode (no loading) mode of background tabs. The goal here is
to collect metrics to compare with other behaviours.

This will be removed once the metrics have been collected.

[sky, 2015-05-11 20:31:52]

LGTM

[Georges Khalil, 2015-05-11 20:32:20]

The CQ bit was checked by georgesak@chromium.org

[commit-bot: I haz the power, 2015-05-11 20:33:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1137033004/1

[Georges Khalil, 2015-05-11 20:58:54]

The CQ bit was unchecked by georgesak@chromium.org

[Georges Khalil, 2015-05-11 21:02:36]

The CQ bit was checked by georgesak@chromium.org

[Georges Khalil, 2015-05-11 21:02:37]

The patchset sent to the CQ was uploaded after l-g-t-m from sky@chromium.org
Link to the patchset: https://codereview.chromium.org/1137033004/#ps20001
(title: "Change experiment name to the new/correct one.")

[commit-bot: I haz the power, 2015-05-11 21:05:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1137033004/20001

[commit-bot: I haz the power, 2015-05-11 22:00:05]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-11 22:00:54]

Patchset 2 (id:??) landed as
https://crrev.com/1912f4a4c9126ed44b1d660cb4451be204738433
Cr-Commit-Position: refs/heads/master@{#329245}