Run microtasks at the end of each worker task.

LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeysession-release-noreference.html

Index: LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeysession-release-noreference.html
diff --git a/LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeysession-release-noreference.html b/LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeysession-release-noreference.html
index 9df6f048b2a6cf521def7eab70fa9f523b265fe9..ebe7ad2953ed7e76bb9b9a003c1ca578db5b6770 100644
--- a/LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeysession-release-noreference.html
+++ b/LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeysession-release-noreference.html
@@ -33,30 +33,24 @@
                 MediaKeys.create('org.w3.clearkey').then(function(result) {
                     mediaKeys = result;
 
-                    // Verify MediaKeys are not an ActiveDOMObject. However, the
-                    // PromiseResolver objects used by MediaKeys/MediaKeySession
-                    // are ActiveDOMObjects, and they stay active until the end
-                    // of the associated then/catch function.
-                    assert_equals(numActiveDOMObjectsCreated(), 1, 'MediaKeys.create()');
+                    // Verify MediaKeys are not an ActiveDOMObject.
+                    assert_equals(numActiveDOMObjectsCreated(), 0, 'MediaKeys.create()');
 
                     return mediaKeys.createSession(initDataType, initData);
                 }).then(function(result) {
                     mediaKeySession1 = result;
                     assert_true(mediaKeySession1.sessionId && mediaKeySession1.sessionId.length > 0);
-                    // Should be 1 MediaKeySession + 1 PromiseResolver from the
-                    // last createSession().
-                    assert_equals(numActiveDOMObjectsCreated(), 2, 'mediaKeys.createSession(1)');
+                    // Should be 1 MediaKeySession.
+                    assert_equals(numActiveDOMObjectsCreated(), 1, 'mediaKeys.createSession(1)');
                     return mediaKeys.createSession(initDataType, initData);
                 }).then(function(result) {
                     mediaKeySession2 = result;
                     assert_true(mediaKeySession2.sessionId && mediaKeySession2.sessionId.length > 0);
-                    // Should be 2 MediaKeySessions + 1 PromiseResolver from the
-                    // last createSession().
-                    assert_equals(numActiveDOMObjectsCreated(), 3, 'mediaKeys.createSession(2)');
+                    // Should be 2 MediaKeySessions.
+                    assert_equals(numActiveDOMObjectsCreated(), 2, 'mediaKeys.createSession(2)');
                 }).then(function(result) {
                     // Run gc(). All sessions should remain as we have a
-                    // reference to each one. However, running gc()
-                    // asynchronously should free up the last PromiseResolver.
+                    // reference to each one.
                     return createGCPromise();
                 }).then(function(result) {
                     // Should be just the 2 MediaKeySessions.