Add CoreClasses

pkg/compiler/lib/src/ssa/types.dart

Index: pkg/compiler/lib/src/ssa/types.dart
diff --git a/pkg/compiler/lib/src/ssa/types.dart b/pkg/compiler/lib/src/ssa/types.dart
index c8a39fa08dbdedd3cde53025d6ca097e62a8ad7d..a34e60b9a7e971e5a7809b53bf8ab4fd3b171a5f 100644
--- a/pkg/compiler/lib/src/ssa/types.dart
+++ b/pkg/compiler/lib/src/ssa/types.dart
@@ -57,11 +57,12 @@ class TypeMaskFactory {
   static TypeMask fromNativeType(type, Compiler compiler) {
     ClassWorld classWorld = compiler.world;
     JavaScriptBackend backend = compiler.backend;
+    CoreClasses coreClasses = compiler.coreClasses;
     if (type == native.SpecialType.JsObject) {
-      return new TypeMask.nonNullExact(compiler.objectClass, classWorld);
+      return new TypeMask.nonNullExact(coreClasses.objectClass, classWorld);
     } else if (type.isVoid) {
       return backend.nullType;
-    } else if (type.element == compiler.nullClass) {
+    } else if (type.element == coreClasses.nullClass) {
       return backend.nullType;
     } else if (type.treatAsDynamic) {
       return backend.dynamicType;