feat(facade): add ListWrapper.toJSON method

modules/angular2/src/facade/collection.dart

@@ -1,9 +1,12 @@
 library facade.collection;
 
 import 'dart:collection' show IterableBase, Iterator;
+import 'dart:convert' show JsonEncoder;
 export 'dart:core' show Map, List, Set;
 import 'dart:math' show max, min;
 
+var jsonEncoder = new JsonEncoder();
+
 class MapIterator extends Iterator<List> {
   final Iterator _iterator;
   final Map _map;
@@ -170,6 +173,10 @@ class ListWrapper {
     }
   }
 
+  static String toJSON(List l) {
+    return jsonEncoder.convert(l);
+  }
+
   // JS splice, slice, fill functions can take start < 0 which indicates a position relative to
   // the end of the list
   static int _startOffset(List l, int start) {

modules/angular2/src/facade/collection.ts

@@ -238,6 +238,8 @@ export class ListWrapper {
     }
   }
   static toString<T>(l: List<T>): string { return l.toString(); }
+  static toJSON<T>(l: List<T>): string { return JSON.stringify(l); }
+
 }
 
 export function isListLikeIterable(obj): boolean {