feat(query_list): delegate toString to _results array

Closes #3004

modules/angular2/src/core/compiler/query_list.dart

@@ -108,6 +108,9 @@ class QueryList<T> extends Object
   int get length => _results.length;
   T get first => _results.first;
   T get last => _results.last;
+  String toString() {
+    return _results.toString();
+  }
 
   List map(fn(T)) {
     // Note: we need to return a list instead of iterable to match JS.

modules/angular2/src/core/compiler/query_list.ts

@@ -97,6 +97,8 @@ export class QueryList<T> {
 
   removeCallback(callback: () => void): void { ListWrapper.remove(this._callbacks, callback); }
 
+  toString(): string { return this._results.toString(); }
+
   get length(): number { return this._results.length; }
   get first(): T { return ListWrapper.first(this._results); }
   get last(): T { return ListWrapper.last(this._results); }