Mention default and minimum for ExtensionCacheSize policy.

Mention default and minimum for ExtensionCacheSize policy.

This expands the documentation on the protobuf definition for the
ExtensionCacheSize policy to mention the minimum allowed value and the
default.

BUG=none

Committed: https://crrev.com/7d4bbed5f47a77946f4fb07f3ccc3a32ecec0d9c
Cr-Commit-Position: refs/heads/master@{#330063}

[Mattias Nissler (ping if slow), 2015-05-13 08:50:43]

mnissler@chromium.org changed reviewers:
+ bartfab@chromium.org

[Mattias Nissler (ping if slow), 2015-05-13 08:50:44]

Please review.

[Mattias Nissler (ping if slow), 2015-05-13 08:51:05]

+binzhao@ to CC

[bartfab (slow), 2015-05-13 12:34:37]

The CQ bit was checked by bartfab@chromium.org

[bartfab (slow), 2015-05-13 12:34:38]

lgtm

[commit-bot: I haz the power, 2015-05-13 12:35:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1123253004/1

[Mattias Nissler (ping if slow), 2015-05-13 12:52:45]

The CQ bit was unchecked by mnissler@chromium.org

[Mattias Nissler (ping if slow), 2015-05-13 12:52:59]

Stopping CQ to give Bin a chance to take a look.

[Bin, 2015-05-14 00:03:31]

binzhao@chromium.org changed reviewers:
+ binzhao@chromium.org

[Bin, 2015-05-14 00:03:32]

lgtm

[Mattias Nissler (ping if slow), 2015-05-15 07:48:29]

The CQ bit was checked by mnissler@chromium.org

[commit-bot: I haz the power, 2015-05-15 07:48:46]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1123253004/1

[commit-bot: I haz the power, 2015-05-15 08:19:55]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-15 08:20:37]

Patchset 1 (id:??) landed as
https://crrev.com/7d4bbed5f47a77946f4fb07f3ccc3a32ecec0d9c
Cr-Commit-Position: refs/heads/master@{#330063}