Tweaks to improve performance of type-inference.

pkg/compiler/lib/src/world.dart

Index: pkg/compiler/lib/src/world.dart
diff --git a/pkg/compiler/lib/src/world.dart b/pkg/compiler/lib/src/world.dart
index 8fd7e6c9724f481bbbd36bf24bf96d83c1769c63..22adbfa033afd83fd2c540b5b9a643152b80edfd 100644
--- a/pkg/compiler/lib/src/world.dart
+++ b/pkg/compiler/lib/src/world.dart
@@ -310,6 +310,8 @@ class World implements ClassWorld {
   /// Returns `true` if all directly instantiated classes that implement [cls]
   /// extend it.
   bool hasOnlySubclasses(ClassElement cls) {
+    // TODO(johnniwinther): move this to ClassSet?
+    if (cls == objectClass) return true;
     Iterable<ClassElement> subtypes = strictSubtypesOf(cls);
     if (subtypes == null) return true;
     Iterable<ClassElement> subclasses = strictSubclassesOf(cls);