Add EmbedRoot to ViewManagerService.

mojo/services/view_manager/view_manager_service_impl.cc

Index: mojo/services/view_manager/view_manager_service_impl.cc
diff --git a/mojo/services/view_manager/view_manager_service_impl.cc b/mojo/services/view_manager/view_manager_service_impl.cc
index ee2c795001ded8b944f3c016b77010483627373c..96cf1021eabcee262b2b57231782b32b16d08949 100644
--- a/mojo/services/view_manager/view_manager_service_impl.cc
+++ b/mojo/services/view_manager/view_manager_service_impl.cc
@@ -726,6 +726,11 @@ void ViewManagerServiceImpl::SetNodeVisibility(
 void ViewManagerServiceImpl::Embed(const String& url,
                                    Id transport_node_id,
                                    const Callback<void(bool)>& callback) {
+  if (NodeIdFromTransportId(transport_node_id) == InvalidNodeId()) {
+    root_node_manager_->EmbedRoot(url);
+    callback.Run(true);
+    return;
+  }
   bool success = CanEmbed(transport_node_id);
   if (success) {
     // Only allow a node to be the root for one connection.