fix(class): correctly clean up on destroy

Fixes #3249
Closes #3256

modules/angular2/src/directives/class.ts

@@ -28,8 +28,11 @@ import {ListWrapper, StringMapWrapper, isListLikeIterable} from 'angular2/src/fa
  * </div>
  * ```
  */
-@Directive(
-    {selector: '[class]', lifecycle: [LifecycleEvent.onCheck], properties: ['rawClass: class']})
+@Directive({
+  selector: '[class]',
+  lifecycle: [LifecycleEvent.onCheck, LifecycleEvent.onDestroy],
+  properties: ['rawClass: class']
+})
 export class CSSClass {
   _pipe: Pipe;
   _rawClass;
@@ -58,6 +61,8 @@ export class CSSClass {
     }
   }
 
+  onDestroy(): void { this._cleanupClasses(this._rawClass); }
+
   private _cleanupClasses(rawClassVal): void {
     if (isPresent(rawClassVal)) {
       if (isListLikeIterable(rawClassVal)) {

modules/angular2/test/directives/class_spec.ts

@@ -14,13 +14,36 @@ import {
   xit,
 } from 'angular2/test_lib';
 import {List, ListWrapper, StringMapWrapper} from 'angular2/src/facade/collection';
-import {Component, View} from 'angular2/angular2';
+import {Component, View, NgFor, bind} from 'angular2/angular2';
 import {DOM} from 'angular2/src/dom/dom_adapter';
 import {CSSClass} from 'angular2/src/directives/class';
+import {APP_VIEW_POOL_CAPACITY} from 'angular2/src/core/compiler/view_pool';
 
 export function main() {
   describe('binding to CSS class list', () => {
 
+    describe('viewpool support', () => {
+      beforeEachBindings(() => { return [bind(APP_VIEW_POOL_CAPACITY).toValue(100)]; });
+
+      it('should clean up when the directive is destroyed',
+         inject([TestComponentBuilder, AsyncTestCompleter], (tcb: TestComponentBuilder, async) => {
+           var template = '<div *ng-for="var item of items" [class]="item"></div>';
+           tcb.overrideTemplate(TestComponent, template)
+               .createAsync(TestComponent)
+               .then((rootTC) => {
+                 rootTC.componentInstance.items = [['0']];
+                 rootTC.detectChanges();
+                 rootTC.componentInstance.items = [['1']];
+                 rootTC.detectChanges();
+                 expect(rootTC.componentViewChildren[1].nativeElement.className)
+                     .toEqual('ng-binding 1');
+
+                 async.done();
+               });
+         }));
+    });
+
+
     describe('expressions evaluating to objects', () => {
 
       it('should add classes specified in an object literal',
@@ -344,9 +367,10 @@ export function main() {
 }
 
 @Component({selector: 'test-cmp'})
-@View({directives: [CSSClass]})
+@View({directives: [CSSClass, NgFor]})
 class TestComponent {
   condition: boolean = true;
+  items: any[];
   arrExpr: List<string> = ['foo'];
   objExpr = {'foo': true, 'bar': false};
   strExpr = 'foo';