ONC: AllowOnlyPolicyNetworksToConnect

This CL maps AllowOnlyPolicyNetworksToConnect to only allowing users
to connect to managed networks.

BUG=208378

Review URL: https://codereview.chromium.org/1433423003

Cr-Commit-Position: refs/heads/master@{#359542}
diff --git a/components/onc/onc_constants.h b/components/onc/onc_constants.h
index d773933..f0fb7ec 100644
--- a/components/onc/onc_constants.h
+++ b/components/onc/onc_constants.h
@@ -429,6 +429,7 @@
 
 namespace global_network_config {
 ONC_EXPORT extern const char kAllowOnlyPolicyNetworksToAutoconnect[];
+ONC_EXPORT extern const char kAllowOnlyPolicyNetworksToConnect[];
 ONC_EXPORT extern const char kDisableNetworkTypes[];
 }  // global_network_config