Add device policy to disallow shutdown

chrome/browser/chromeos/policy/proto/chrome_device_policy.proto

Index: chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
diff --git a/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto b/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
index f5c1a4cd9b669076f92b61343f8bb82b52c28458..f8ad412d9324eac56525f21c6ba87ffb685904cb 100644
--- a/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
+++ b/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
@@ -583,6 +583,13 @@ message SAMLSettingsProto {
   optional bool transfer_saml_cookies = 1;
 }
 
+message RebootOnShutdownProto {
+  // Determines whether the device may be shut down. If this flag is set to

[bartfab (slow), 2014/12/15 18:01:56]

Nit: Now that the policy was renamed, I think this comment should be reworded to
something like:

Determines whether the device automatically reboots whenever the user shuts it
down. This policy affects shutdowns triggered from the UI only. If the user
shuts down the device using the power button, it will not automatically reboot,
even if the policy is enabled.

[cschuet (SLOW), 2014/12/16 10:02:07]

Done.

+  // true, shutdown is forbidden and UI elements trigger a device reboot instead
+  // of a power off. This policy controls shutdown via the UI only.
+  optional bool reboot_on_shutdown = 1 [default = false];
+}
+
 message ChromeDeviceSettingsProto {
   optional DevicePolicyRefreshRateProto device_policy_refresh_rate = 1;
   optional UserWhitelistProto user_whitelist = 2;
@@ -617,4 +624,5 @@ message ChromeDeviceSettingsProto {
   optional AutoCleanupSettigsProto auto_clean_up_settings = 31;
   optional SystemSettingsProto system_settings = 32;
   optional SAMLSettingsProto saml_settings = 33;
+  optional RebootOnShutdownProto reboot_on_shutdown = 34;
 }