Fixes for exports

tool/input_sdk/private/utils.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart._utils;
 
 import 'dart:_foreign_helper' show JS;
 
 /// This library defines a set of general javascript utilities for us
 /// by the Dart runtime.
@@ skipping 79 matching lines @@
   }
 })(#, #)''', to, from);
 
 defineMemoizedGetter(obj, String name, getter) =>
     JS('', '''((obj, name, getter) => {
   return defineLazyProperty(obj, name, {get: getter});
 })(#, #, #)''', obj, name, getter);
 
 copyTheseProperties(to, from, names) => JS('', '''((to, from, names) => {
   for (let name of names) {
-    defineProperty(to, name, getOwnPropertyDescriptor(from, name));
+    var desc = getOwnPropertyDescriptor(from, name);
+    if (desc != void 0) {
+      defineProperty(to, name, desc);
+    } else {
+      defineLazyProperty(to, name, () => from[name]);
+    }
   }
   return to;
 })(#, #, #)''', to, from, names);
 
 /// Copy properties from source to destination object.
 /// This operation is commonly called `mixin` in JS.
 copyProperties(to, from) => JS('', '''((to, from) => {
   return copyTheseProperties(to, from, getOwnNamesAndSymbols(from));
 })(#, #)''', to, from);
 
 /// Exports from one Dart module to another.
 // TODO(ochafik): Re-introduce a @JS annotation in the SDK (same as package:js)
 // so that this is named 'export' in JavaScript.
 export_(to, from, show, hide) => JS('', '''((to, from, show, hide) => {
-  if (show == void 0) {
+  if (show == void 0 || show.length == 0) {
     show = getOwnNamesAndSymbols(from);
   }
   if (hide != void 0) {
     var hideMap = new Set(hide);
     show = show.filter((k) => !hideMap.has(k));
   }
   return copyTheseProperties(to, from, show);
 })(#, #, #, #)''', to, from, show, hide);