Bring up the service isolate and use it for package resolution in gen_snapshot

runtime/bin/dartutils.cc

Index: runtime/bin/dartutils.cc
diff --git a/runtime/bin/dartutils.cc b/runtime/bin/dartutils.cc
index 3c01e64f8f7cbd986fb0083a436aba90869f5d91..be37bc02d316e36b1b53a81db56d785500556f61 100644
--- a/runtime/bin/dartutils.cc
+++ b/runtime/bin/dartutils.cc
@@ -663,7 +663,8 @@ Dart_Handle DartUtils::PrepareBuiltinLibrary(Dart_Handle builtin_lib,
     // Wait for the service isolate to initialize the load port.
     Dart_Port load_port = Dart_ServiceWaitForLoadPort();
     if (load_port == ILLEGAL_PORT) {
-      return NewDartUnsupportedError("Service did not return load port.");
+      return Dart_NewUnhandledExceptionError(
+          NewDartUnsupportedError("Service did not return load port."));
     }
     result = Builtin::SetLoadPort(load_port);
     RETURN_IF_ERROR(result);