Add |device_heartbeat_settings| to device policy proto

Add |device_heartbeat_settings| to device policy proto

This CL adds |device_heartbeat_settings| to the device policy proto.
We accidentally added |device_heartbeat_settings| with index 34 on
the server and |reboot_on_shutdown| with the same index on the client.
To resolve this conflict, one of the two settings needs to change
index. Since |device_heartbeat_settings| is not being read or written
by anyone yet, it is the one to move.

We must avoid such conflicts in the future by adding all policies on
the client-side first and syncing the resulting proto to the server.

In general, new policies should be added to the device policy proto
and policy_templates.json at the same time. As an emergency fix, this
CL gets a free pass for that rule as it is an emergency fix.

BUG=430908
TEST=None

Committed: https://crrev.com/2d7b3827311376842db9481bae84b0150a72017a
Cr-Commit-Position: refs/heads/master@{#314346}

[bartfab (slow), 2015-02-02 12:29:11]

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

[bartfab (slow), 2015-02-02 12:29:12]

Hi Drew,

Please take a look.

[Andrew T Wilson (Slow), 2015-02-03 15:48:42]

lgtm

[bartfab (slow), 2015-02-03 15:52:18]

The CQ bit was checked by bartfab@chromium.org

[commit-bot: I haz the power, 2015-02-03 15:52:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/887423002/2

[commit-bot: I haz the power, 2015-02-03 16:28:28]

Committed patchset #2 (id:2)

[commit-bot: I haz the power, 2015-02-03 16:29:27]

Patchset 2 (id:??) landed as
https://crrev.com/2d7b3827311376842db9481bae84b0150a72017a
Cr-Commit-Position: refs/heads/master@{#314346}