update_engine: Indicate existence of owner instead of owner's email in log.

Logging the device owner's email is possibly a PII, so instead log
whether the device has a owner as a boolean value.

Enterprise devices do not have a device owner.

The variable var_has_owner is dependent on DevicePolicy::GetOwner().

BUG=chromium:973108
TEST=unittest

Change-Id: I535f664a4fcf75c6102346b8566605710b062255
Reviewed-on: https://chromium-review.googlesource.com/1660911
Tested-by: Jae Hoon Kim <kimjae@chromium.org>
Commit-Ready: Jae Hoon Kim <kimjae@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Amin Hassani <ahassani@chromium.org>
diff --git a/update_manager/device_policy_provider.h b/update_manager/device_policy_provider.h
index 873282e..b68fe96 100644
--- a/update_manager/device_policy_provider.h
+++ b/update_manager/device_policy_provider.h
@@ -66,9 +66,9 @@
   virtual Variable<std::set<chromeos_update_engine::ConnectionType>>*
   var_allowed_connection_types_for_update() = 0;
 
-  // Variable stating the name of the device owner. For enterprise enrolled
-  // devices, this will be an empty string.
-  virtual Variable<std::string>* var_owner() = 0;
+  // Variable stating whether the device has an owner. For enterprise enrolled
+  // devices, this will be false as the device owner has an empty string.
+  virtual Variable<bool>* var_has_owner() = 0;
 
   virtual Variable<bool>* var_http_downloads_enabled() = 0;