Implement modular compilation

tool/input_sdk/private/ddc_runtime/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.
 part of dart._runtime;
 
 /// This library defines a set of general javascript utilities for us
 /// by the Dart runtime.
 // TODO(ochafik): Rewrite some of these in Dart when possible.
 
 final defineProperty = JS('', 'Object.defineProperty');
@@ skipping 65 matching lines @@
 void defineLazy(to, from) => JS('', '''(() => {
   for (let name of $getOwnNamesAndSymbols($from)) {
     $defineLazyProperty($to, name, $getOwnPropertyDescriptor($from, name));
   }
 })()''');
 
 defineMemoizedGetter(obj, String name, getter) => JS('', '''(() => {
   return $defineLazyProperty($obj, $name, {get: $getter});
 })()''');
 
+
+// TODO(jmesserly): don't stomp on native Symbol.iterator.
+// We need to find a better solution for this.
+// See: https://github.com/dart-lang/dev_compiler/issues/487
 copyTheseProperties(to, from, names) => JS('', '''(() => {
   for (let name of $names) {
-    var desc = $getOwnPropertyDescriptor($from, name);
+    let desc = $getOwnPropertyDescriptor($from, name);
     if (desc != void 0) {
+      if (name == Symbol.iterator) {
+        // On native types, Symbol.iterator may already be present.
+        let existing = $getOwnPropertyDescriptor($to, name);
+        if (existing != null) {
+          if (existing.writable) $to[Symbol.iterator] = desc.value;
+          continue;
+        }
+      }
       $defineProperty($to, name, desc);
     } else {
       $defineLazyProperty($to, name, () => $from[name]);
     }
   }
   return $to;
 })()''');
 
 /// Copy properties from source to destination object.
 /// This operation is commonly called `mixin` in JS.
 copyProperties(to, from) => JS('', '''(() => {
   return $copyTheseProperties($to, $from, $getOwnNamesAndSymbols($from));
 })()''');
-
-/// Exports from one Dart module to another.
-@JSExportName('export')
-export_(to, from, show, hide) => JS('', '''(() => {
-  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);
-})()''');