Add hook to register global object

sdk/lib/_internal/js_runtime/lib/js_helper.dart

Index: sdk/lib/_internal/js_runtime/lib/js_helper.dart
diff --git a/sdk/lib/_internal/js_runtime/lib/js_helper.dart b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
index d98ee1c06ac5ec3e22d8020f75a6104240cc258e..66291bd6b8a3ce6c7acf84f01ef80ddb9a72f73f 100644
--- a/sdk/lib/_internal/js_runtime/lib/js_helper.dart
+++ b/sdk/lib/_internal/js_runtime/lib/js_helper.dart
@@ -3812,3 +3812,7 @@ class _UnreachableError extends AssertionError {
 void assertUnreachable() {
   throw new _UnreachableError();
 }
+
+// Hook to register new global object if necessary.
+// This is currently a no-op in dart2js.
+void registerGlobalObject(object) {}