fix(zonespec): don't throw and exception when setInterval is called within a async test zone (#641)

Author: vikerman

Diff for: lib/zone-spec/async-test.ts

@@ -61,15 +61,6 @@ class AsyncTestZoneSpec implements ZoneSpec {
     return false;
   }
 
-  onScheduleTask(delegate: ZoneDelegate, currentZone: Zone, targetZone: Zone, task: Task): Task {
-    if (task.type == 'macroTask' && task.source == 'setInterval') {
-      this._failCallback('Cannot use setInterval from within an async zone test.');
-      return;
-    }
-
-    return delegate.scheduleTask(targetZone, task);
-  }
-
   onHasTask(delegate: ZoneDelegate, current: Zone, target: Zone, hasTaskState: HasTaskState) {
     delegate.hasTask(target, hasTaskState);
     if (hasTaskState.change == 'microTask') {

Diff for: test/zone-spec/async-test.spec.ts

@@ -259,21 +259,22 @@ describe('AsyncTestZoneSpec', function() {
              });
            }));
 
-  it('should fail if setInterval is used', (done) => {
+  it('should not fail if setInterval is used and canceled', (done) => {
     const testZoneSpec = new AsyncTestZoneSpec(
         () => {
-          done.fail('expected failCallback to be called');
+          done();
         },
         (err) => {
-          expect(err).toEqual('Cannot use setInterval from within an async zone test.');
-          done();
+          done.fail('async zone called failCallback unexpectedly');
         },
         'name');
 
     const atz = Zone.current.fork(testZoneSpec);
 
     atz.run(function() {
-      setInterval(() => {}, 100);
+      let id = setInterval(() => {
+        clearInterval(id);
+      }, 100);
     });
   });