[Sync] Make syncer commands avoid posting tasks on threads with no work to do

chrome/browser/sync/test/engine/fake_model_safe_worker_registrar.cc

Index: chrome/browser/sync/test/engine/fake_model_safe_worker_registrar.cc
diff --git a/chrome/browser/sync/test/engine/fake_model_safe_worker_registrar.cc b/chrome/browser/sync/test/engine/fake_model_safe_worker_registrar.cc
index 15a4d45f9b0f42d8bbdef01cc48f4fdce26e9aff..21ab0616a8ba47c666b9edcf5b9ffe5208946b1e 100644
--- a/chrome/browser/sync/test/engine/fake_model_safe_worker_registrar.cc
+++ b/chrome/browser/sync/test/engine/fake_model_safe_worker_registrar.cc
@@ -15,6 +15,8 @@ FakeModelSafeWorkerRegistrar::FakeModelSafeWorkerRegistrar(
        it != routes_.end(); ++it) {
     groups.insert(it->second);
   }
+  // Sessions always expect a passive worker to be present.
+  groups.insert(GROUP_PASSIVE);
 
   for (std::set<ModelSafeGroup>::const_iterator it = groups.begin();
        it != groups.end(); ++it) {