Add |device_heartbeat_settings| to device policy proto

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 5d75fb87570ab83ddc460bfde1ce00b7f96f97d1..80c5467d256893981074f2e7957fd9fbf607acc5 100644
--- a/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
+++ b/chrome/browser/chromeos/policy/proto/chrome_device_policy.proto
@@ -594,6 +594,17 @@ message RebootOnShutdownProto {
   optional bool reboot_on_shutdown = 1 [default = false];
 }
 
+// Settings that control whether a device would send heartbeat messages to GCM,
+// and how frequently to send these.
+message DeviceHeartbeatSettingsProto {
+  // Whether the device should send heartbeat messages. The default is false.
+  optional bool heartbeat_enabled = 1 [default = false];
+
+  // How frequently devices send heartbeats back to server. The unit is in
+  // milliseconds. The default is 2 minutes.
+  optional int64 heartbeat_frequency = 2 [default = 120000];
+}
+
 message ChromeDeviceSettingsProto {
   optional DevicePolicyRefreshRateProto device_policy_refresh_rate = 1;
   optional UserWhitelistProto user_whitelist = 2;
@@ -631,4 +642,5 @@ message ChromeDeviceSettingsProto {
   optional SystemSettingsProto system_settings = 32;
   optional SAMLSettingsProto saml_settings = 33;
   optional RebootOnShutdownProto reboot_on_shutdown = 34;
+  optional DeviceHeartbeatSettingsProto device_heartbeat_settings = 35;
 }