Docserver: Cache the samples.

Docserver: Cache the samples in the API reference documentation.
This is probably the main source of Docserver slowness. Doing so
also leads to some nice cleanups, like removing the odd samples
getter and making samples resolution asynchronous.

R=rockot@chromium.org
BUG=415309
Committed: https://crrev.com/81ab7b017ba2fa14ec5b962d173bf39c4151b10a
Cr-Commit-Position: refs/heads/master@{#299973}

[not at google - send to devlin, 2014-10-15 23:32:41]

kalman@chromium.org changed reviewers:
+ rockot@chromium.org

[Ken Rockot(use gerrit already), 2014-10-16 19:09:49]

lgtm

[not at google - send to devlin, 2014-10-16 19:59:57]

The CQ bit was checked by kalman@chromium.org

[commit-bot: I haz the power, 2014-10-16 20:00:50]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/656673003/20001

[commit-bot: I haz the power, 2014-10-16 20:55:11]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2014-10-16 20:56:26]

Patchset 2 (id:??) landed as
https://crrev.com/81ab7b017ba2fa14ec5b962d173bf39c4151b10a
Cr-Commit-Position: refs/heads/master@{#299973}