Fixed experimental app list pagination indicator.

Fixed experimental app list pagination indicator.

Was previously highlighting the wrong page (regressed in r293066) due to
the page indices not starting from 0.

ContentsSwitcherView now uses a map, not a vector, so buttons can have
arbitrary indices.

BUG=411769
Committed: https://crrev.com/30f9a0e253bc3a325ec85ff768d03c2f46a72244
Cr-Commit-Position: refs/heads/master@{#293884}

[Matt Giuca, 2014-09-08 06:16:13]

mgiuca@chromium.org changed reviewers:
+ calamity@chromium.org

[calamity, 2014-09-09 00:49:18]

lgtm

[Matt Giuca, 2014-09-09 00:56:34]

The CQ bit was checked by mgiuca@chromium.org

[commit-bot: I haz the power, 2014-09-09 00:58:42]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/mgiuca@chromium.org/554553002/1

[commit-bot: I haz the power, 2014-09-09 07:19:06]

Committed patchset #1 (id:1) as 660a2a314dbbe5d4466014352cac65eaf739c655

[commit-bot: I haz the power, 2014-09-10 03:51:36]

Patchset 1 (id:??) landed as
https://crrev.com/30f9a0e253bc3a325ec85ff768d03c2f46a72244
Cr-Commit-Position: refs/heads/master@{#293884}