fixes #202, check IndexExpression

lib/runtime/dart/_internal.js

 var _internal = dart.defineLibrary(_internal, {});
 var core = dart.import(core);
 var collection = dart.import(collection);
 var math = dart.lazyImport(math);
 var _interceptors = dart.lazyImport(_interceptors);
 var _js_primitives = dart.lazyImport(_js_primitives);
 (function(exports, core, collection, math, _interceptors, _js_primitives) {
   'use strict';
   class EfficientLength extends core.Object {}
   let ListIterable$ = dart.generic(function(E) {
@@ skipping 1703 matching lines @@
     constructors: () => ({_ListIndicesIterable: [_ListIndicesIterable, [core.List]]}),
     methods: () => ({[core.$elementAt]: [core.int, [core.int]]})
   });
   let _values = dart.JsSymbol('_values');
   let ListMapView$ = dart.generic(function(E) {
     class ListMapView extends core.Object {
       ListMapView(values) {
         this[_values] = values;
       }
       get(key) {
-        return this.containsKey(key) ? this[_values][core.$get](key) : null;
+        return this.containsKey(key) ? this[_values][core.$get](dart.as(key, core.int)) : null;
       }
       get length() {
         return this[_values][core.$length];
       }
       get values() {
         return new (SubListIterable$(E))(this[_values], 0, null);
       }
       get keys() {
         return new _ListIndicesIterable(this[_values]);
       }
@@ skipping 610 matching lines @@
   exports.ReversedListIterable = ReversedListIterable;
   exports.UnmodifiableListError = UnmodifiableListError;
   exports.NonGrowableListError = NonGrowableListError;
   exports.makeListFixedLength = makeListFixedLength;
   exports.Lists = Lists;
   exports.printToConsole = printToConsole;
   exports.Sort = Sort;
   exports.Symbol = Symbol;
   exports.POWERS_OF_TEN = POWERS_OF_TEN;
 })(_internal, core, collection, math, _interceptors, _js_primitives);