Add annotations on native fields and methods

sdk/lib/_internal/compiler/implementation/lib/js_array.dart

Index: sdk/lib/_internal/compiler/implementation/lib/js_array.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/js_array.dart b/sdk/lib/_internal/compiler/implementation/lib/js_array.dart
index ec4d1a3fa1f5dbad6c492dbca633aba691294275..c5fbcb6b08a3201a75ec66413d5e370ccbabd2d2 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/js_array.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/js_array.dart
@@ -78,7 +78,7 @@ class JSArray<E> implements List<E> {
       throw new RangeError.value(length);
     }
     if (length < 0) throw new ArgumentError(length);
-    return JS('List', r'#.slice(#, #)', this, start, end);
+    return JS('=List', r'#.slice(#, #)', this, start, end);
   }
 
   void insertRange(int start, int length, [E initialValue]) {