feat(NgFor): $last property support

Makes a new `$last` property available during the loop with a boolean
showing if it's the last item in the iteration.

closes: angular#3102

Closes angular#3991

Author: alfonso-presa

modules/angular2/src/core/directives/ng_for.ts

@@ -9,7 +9,8 @@ import {isPresent, isBlank} from 'angular2/src/core/facade/lang';
  * to the current item from the iterable.
  *
  * It is possible to alias the `index` to a local variable that will be set to the current loop
- * iteration in the template context.
+ * iteration in the template context, and also to alias the 'last' to a local variable that will
+ * be set to a boolean indicating if the item is the last one in the iteration
  *
  * When the contents of the iterator changes, `NgFor` makes the corresponding changes to the DOM:
  *
@@ -76,6 +77,10 @@ export class NgFor {
     for (var i = 0; i < insertTuples.length; i++) {
       this._perViewChange(insertTuples[i].view, insertTuples[i].record);
     }
+
+    for (var i = 0, ilen = this.viewContainer.length; i < ilen; i++) {
+      this.viewContainer.get(i).setLocal('last', i === ilen - 1);
+    }
   }
 
   private _perViewChange(view, record) {

modules/angular2/test/core/directives/ng_for_spec.ts

@@ -252,6 +252,25 @@ export function main() {
              });
        }));
 
+    it('should display last item correctly',
+       inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
+         var template =
+             '<div><copy-me template="ng-for: var item of items; var isLast=last">{{isLast.toString()}}</copy-me></div>';
+
+         tcb.overrideTemplate(TestComponent, template)
+             .createAsync(TestComponent)
+             .then((rootTC) => {
+               rootTC.componentInstance.items = [0, 1, 2];
+               rootTC.detectChanges();
+               expect(rootTC.nativeElement).toHaveText('falsefalsetrue');
+
+               rootTC.componentInstance.items = [2, 1];
+               rootTC.detectChanges();
+               expect(rootTC.nativeElement).toHaveText('falsetrue');
+               async.done();
+             });
+       }));
+
   });
 }