Expose signing key from cloud policy stores

chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.cc

Index: chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.cc
diff --git a/chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.cc b/chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.cc
index 0f600faa3585e00c74a81d6c712766d0195589fb..d71612635af40e58e21b063357f02a57373eef03 100644
--- a/chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.cc
+++ b/chrome/browser/chromeos/policy/device_cloud_policy_store_chromeos.cc
@@ -163,6 +163,10 @@ void DeviceCloudPolicyStoreChromeOS::UpdateFromService() {
     }
     policy_map_.Swap(&new_policy_map);
 
+    scoped_refptr<ownership::PublicKey> key =
+        device_settings_service_->GetPublicKey();
+    public_key_ = key ? key->as_string() : std::string();
+
     NotifyStoreLoaded();
     return;
   }