feat(testability): Expose function frameworkStabilizers

Closes #5485

modules/angular2/src/core/testability/testability.ts

@@ -15,6 +15,13 @@ import {PromiseWrapper, ObservableWrapper} from 'angular2/src/facade/async';
 export class Testability {
   /** @internal */
   _pendingCount: number = 0;
+  /**
+   * Whether any work was done since the last 'whenStable' callback. This is
+   * useful to detect if this could have potentially destabilized another
+   * component while it is stabilizing.
+   * @internal
+   */
+  _didWork: boolean = false;
   /** @internal */
   _callbacks: Function[] = [];
   /** @internal */
@@ -23,8 +30,10 @@ export class Testability {
 
   /** @internal */
   _watchAngularEvents(_ngZone: NgZone): void {
-    ObservableWrapper.subscribe(_ngZone.onTurnStart,
-                                (_) => { this._isAngularEventPending = true; });
+    ObservableWrapper.subscribe(_ngZone.onTurnStart, (_) => {
+      this._didWork = true;
+      this._isAngularEventPending = true;
+    });
 
     _ngZone.runOutsideAngular(() => {
       ObservableWrapper.subscribe(_ngZone.onEventDone, (_) => {
@@ -38,6 +47,7 @@ export class Testability {
 
   increasePendingRequestCount(): number {
     this._pendingCount += 1;
+    this._didWork = true;
     return this._pendingCount;
   }
 
@@ -55,14 +65,16 @@ export class Testability {
   /** @internal */
   _runCallbacksIfReady(): void {
     if (!this.isStable()) {
+      this._didWork = true;
       return;  // Not ready
     }
 
     // Schedules the call backs in a new frame so that it is always async.
     PromiseWrapper.resolve(null).then((_) => {
       while (this._callbacks.length !== 0) {
-        (this._callbacks.pop())();
+        (this._callbacks.pop())(this._didWork);
       }
+      this._didWork = false;
     });
   }