feat(ng-repeat): set the "$parent" variable to the parent context

fixes #953

Author: vicb

lib/directive/ng_repeat.dart

@@ -173,7 +173,8 @@ class NgRepeat {
       changeFunctions[addition.currentIndex] = (index, previousView) {
         var childScope = _scope.createProtoChild();
         var childContext = _updateContext(childScope.context, index, length)
-            ..[_valueIdentifier] = value;
+            ..[_valueIdentifier] = value
+            ..[r'$parent'] = _scope.context;
         var view = views[index] = _boundViewFactory(childScope);
         _viewPort.insert(view, insertAfter: previousView);
       };

test/directive/ng_repeat_spec.dart

@@ -41,6 +41,20 @@ main() {
       expect(element).toHaveText('ab');
     });
 
+    it(r'should support $parent to access the parent context',
+       (Scope scope, Compiler compiler, Injector injector) {
+      var element = es('<div>'
+                         '<span ng-repeat="list in lists">'
+                           r'<span ng-repeat="i in list">{{$parent.$index}}-{{$index}},</span>'
+                         '</span>'
+                       '</div>');
+      ViewFactory viewFactory = compiler(element, directives);
+      View view = viewFactory(scope, null, element);
+      scope.context['lists'] = [[0, 0, 0], [0]];
+      scope.apply();
+      expect(element).toHaveText('0-0,0-1,0-2,1-0,');
+    });
+
 
     it(r'should set create a list of items', (Scope scope, Compiler compiler, Injector injector) {
       scope.context['items'] = [];