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

lib/runtime/dart/core.js

 var core;
 (function(exports) {
   'use strict';
   class Object {
     constructor() {
       let name = this.constructor.name;
       let init = this[name];
       let result = void 0;
       if (init)
         result = init.apply(this, arguments);
@@ skipping 1056 matching lines @@
       let onError = opts && 'onError' in opts ? opts.onError : null;
       return _js_helper.Primitives.parseInt(source, radix, onError);
     }
   }
   dart.defineNamedConstructor(int, 'fromEnvironment');
   class Invocation extends Object {
     get isAccessor() {
       return dart.notNull(this.isGetter) || dart.notNull(this.isSetter);
     }
   }
+  let $iterator = dart.JsSymbol('$iterator');
   let $join = dart.JsSymbol('$join');
   let Iterable$ = dart.generic(function(E) {
     class Iterable extends Object {
       Iterable() {
       }
       generate(count, generator) {
         if (generator === void 0)
           generator = null;
         if (dart.notNull(count) <= 0)
           return new (_internal.EmptyIterable$(E))();
         return new (exports._GeneratorIterable$(E))(count, generator);
       }
+      [dart.JsSymbol.iterator]() {
+        return new dart.JsIterator(this[$iterator]);
+      }
       [$join](separator) {
         if (separator === void 0)
           separator = "";
         let buffer = new StringBuffer();
         buffer.writeAll(this, separator);
         return dart.toString(buffer);
       }
-      [dart.JsSymbol.iterator]() {
-        var iterator = this.iterator;
-        return {
-          next() {
-            var done = iterator.moveNext();
-            return {done: done, current: done ? void 0 : iterator.current};
-          }
-        };
-      }
     }
     dart.defineNamedConstructor(Iterable, 'generate');
     return Iterable;
   });
   let Iterable = Iterable$();
   let _Generator$ = dart.generic(function(E) {
     let _Generator = dart.typedef('_Generator', () => dart.functionType(E, [int]));
     return _Generator;
   });
   let _Generator = _Generator$();
   let _end = dart.JsSymbol('_end');
   let _start = dart.JsSymbol('_start');
   let _generator = dart.JsSymbol('_generator');
-  let $iterator = dart.JsSymbol('$iterator');
   let $skip = dart.JsSymbol('$skip');
   let $take = dart.JsSymbol('$take');
   let _GeneratorIterable$ = dart.generic(function(E) {
     class _GeneratorIterable extends collection.IterableBase$(E) {
       _GeneratorIterable(end, generator) {
         this[_end] = end;
         this[_start] = 0;
         this[_generator] = dart.as(generator != null ? generator : _GeneratorIterable._id, _Generator$(E));
         super.IterableBase();
       }
@@ skipping 2265 matching lines @@
   exports.CyclicInitializationError = CyclicInitializationError;
   exports.Exception = Exception;
   exports.FormatException = FormatException;
   exports.IntegerDivisionByZeroException = IntegerDivisionByZeroException;
   exports.Expando$ = Expando$;
   exports.Expando = Expando;
   exports.identical = identical;
   exports.identityHashCode = identityHashCode;
   exports.int = int;
   exports.Invocation = Invocation;
+  exports.$iterator = $iterator;
   exports.$join = $join;
   exports.Iterable$ = Iterable$;
   exports.Iterable = Iterable;
-  exports.$iterator = $iterator;
   exports.$skip = $skip;
   exports.$take = $take;
   exports.BidirectionalIterator$ = BidirectionalIterator$;
   exports.BidirectionalIterator = BidirectionalIterator;
   exports.Iterator$ = Iterator$;
   exports.Iterator = Iterator;
   exports.$set = $set;
   exports.$add = $add;
   exports.$checkMutable = $checkMutable;
   exports.$checkGrowable = $checkGrowable;
@@ skipping 58 matching lines @@
   exports.StackTrace = StackTrace;
   exports.Stopwatch = Stopwatch;
   exports.String = String;
   exports.RuneIterator = RuneIterator;
   exports.StringBuffer = StringBuffer;
   exports.StringSink = StringSink;
   exports.Symbol = Symbol;
   exports.Type = Type;
   exports.Uri = Uri;
 })(core || (core = {}));