Makes ViewManagerServiceImpl track a single root

mojo/services/view_manager/window_manager_access_policy.cc

Index: mojo/services/view_manager/window_manager_access_policy.cc
diff --git a/mojo/services/view_manager/window_manager_access_policy.cc b/mojo/services/view_manager/window_manager_access_policy.cc
index 47f4c3a9bea1fd4191907711689d41ab59ec3498..8a477f064d4b5c71ecf7029f874157f1fce3f59e 100644
--- a/mojo/services/view_manager/window_manager_access_policy.cc
+++ b/mojo/services/view_manager/window_manager_access_policy.cc
@@ -66,8 +66,7 @@ bool WindowManagerAccessPolicy::CanSetViewSurfaceId(
   if (delegate_->IsViewRootOfAnotherConnectionForAccessPolicy(view))
     return false;
   return view->id().connection_id == connection_id_ ||
-         (delegate_->GetRootsForAccessPolicy().count(
-              ViewIdToTransportId(view->id())) > 0);
+         (delegate_->IsRootForAccessPolicy(view->id()));
 }
 
 bool WindowManagerAccessPolicy::CanSetViewBounds(const ServerView* view) const {