fixes #130, accept anything with `iterator` in for loops

lib/runtime/dart_runtime.js

 // 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.
 
 var dart, _js_helper, _js_primitives;
 (function (dart) {
   'use strict';
 
   let defineProperty = Object.defineProperty;
   let getOwnPropertyDescriptor = Object.getOwnPropertyDescriptor;
@@ skipping 927 matching lines @@
       case "number":
       case "boolean":
       case "string":
         throw new core.NoSuchMethodError(obj, invocation.memberName,
           invocation.positionalArguments, invocation.namedArguments);
     }
     return obj.noSuchMethod(invocation);
   }
   dart.noSuchMethod = noSuchMethod;
 
+  class JsIterator {
+    constructor(dartIterator) {
+      this.dartIterator = dartIterator;
+    }
+    next() {
+      let i = this.dartIterator;
+      var done = !i.moveNext();
+      return { done: done, value: done ? void 0 : i.current };
+    }
+  }
+  dart.JsIterator = JsIterator;
+
   // TODO(jmesserly): right now this is a sentinel. It should be a type object
   // of some sort, assuming we keep around `dynamic` at runtime.
   dart.dynamic = { toString() { return 'dynamic'; } };
   dart.void = { toString() { return 'void'; } };
   dart.bottom = { toString() { return 'bottom'; } };
 
   dart.global = window || global;
   dart.JsSymbol = Symbol;
 
   // TODO(jmesserly): hack to bootstrap the SDK
   _js_helper = _js_helper || {};
   _js_helper.checkNum = notNull;
 
   _js_primitives = _js_primitives || {};
   _js_primitives.printString = (s) => console.log(s);
 
 })(dart || (dart = {}));