Fixes for exports

lib/runtime/dart/_utils.js

 dart_library.library('dart/_utils', null, /* Imports */[
 ], /* Lazy imports */[
 ], function(exports, dart) {
   'use strict';
   const defineProperty = Object.defineProperty;
   const getOwnPropertyDescriptor = Object.getOwnPropertyDescriptor;
   const getOwnPropertyNames = Object.getOwnPropertyNames;
   const getOwnPropertySymbols = Object.getOwnPropertySymbols;
   const hasOwnProperty = Object.prototype.hasOwnProperty;
   const StrongModeError = (function() {
@@ skipping 50 matching lines @@
   function defineLazy(to, from) {
     for (let name of getOwnNamesAndSymbols(from)) {
       defineLazyProperty(to, name, getOwnPropertyDescriptor(from, name));
     }
   }
   function defineMemoizedGetter(obj, name, getter) {
     return defineLazyProperty(obj, name, {get: getter});
   }
   function copyTheseProperties(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;
   }
   function copyProperties(to, from) {
     return copyTheseProperties(to, from, getOwnNamesAndSymbols(from));
   }
   function export_(to, from, show, hide) {
-    if (show == void 0) {
+    if (show == void 0 || show.length == 0) {

[vsm, 2015/12/01 22:29:51]

Note: show is undefined on a regular export and [] when there is a hide clause.

       show = getOwnNamesAndSymbols(from);
     }
     if (hide != void 0) {
       var hideMap = new Set(hide);
       show = show.filter(k => !hideMap.has(k));
     }
     return copyTheseProperties(to, from, show);
   }
   // Exports:
   exports.defineProperty = defineProperty;
   exports.getOwnPropertyDescriptor = getOwnPropertyDescriptor;
   exports.getOwnPropertyNames = getOwnPropertyNames;
   exports.getOwnPropertySymbols = getOwnPropertySymbols;
   exports.hasOwnProperty = hasOwnProperty;
   exports.StrongModeError = StrongModeError;
   exports.throwStrongModeError = throwStrongModeError;
   exports.throwInternalError = throwInternalError;
   exports.assert_ = assert_;
   exports.getOwnNamesAndSymbols = getOwnNamesAndSymbols;
   exports.safeGetOwnProperty = safeGetOwnProperty;
   exports.defineLazyProperty = defineLazyProperty;
   exports.defineLazy = defineLazy;
   exports.defineMemoizedGetter = defineMemoizedGetter;
   exports.copyTheseProperties = copyTheseProperties;
   exports.copyProperties = copyProperties;
   exports.export_ = export_;
 });