feat(ngFor): Support convenience view local in ngFor

Closes #8013

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

@@ -26,6 +26,8 @@ import {BaseException} from "../../facade/exceptions";
  * `NgFor` provides several exported values that can be aliased to local variables:
  *
  * * `index` will be set to the current loop iteration for each template context.
+ * * `first` will be set to a boolean value indicating whether the item is the first one in the
+ *   iteration.
  * * `last` will be set to a boolean value indicating whether the item is the last one in the
  *   iteration.
  * * `even` will be set to a boolean value indicating whether this item has an even index.
@@ -126,6 +128,7 @@ export class NgFor implements DoCheck {
 
     for (var i = 0, ilen = this._viewContainer.length; i < ilen; i++) {
       var viewRef = <EmbeddedViewRef>this._viewContainer.get(i);
+      viewRef.setLocal('first', i === 0);
       viewRef.setLocal('last', i === ilen - 1);
     }
 

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

@@ -298,6 +298,25 @@ export function main() {
              });
        }));
 
+    it('should display first item correctly',
+       inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
+         var template =
+             '<div><copy-me template="ngFor: var item of items; var isFirst=first">{{isFirst.toString()}}</copy-me></div>';
+
+         tcb.overrideTemplate(TestComponent, template)
+             .createAsync(TestComponent)
+             .then((fixture) => {
+               fixture.debugElement.componentInstance.items = [0, 1, 2];
+               fixture.detectChanges();
+               expect(fixture.debugElement.nativeElement).toHaveText('truefalsefalse');
+
+               fixture.debugElement.componentInstance.items = [2, 1];
+               fixture.detectChanges();
+               expect(fixture.debugElement.nativeElement).toHaveText('truefalse');
+               async.done();
+             });
+       }));
+
     it('should display last item correctly',
        inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
          var template =