Run microtasks at the end of each worker task.

LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeys-with-session.html

Index: LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeys-with-session.html
diff --git a/LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeys-with-session.html b/LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeys-with-session.html
index 9126ac7566c9b1766f649e2dc8c3fd50f6d0f12a..74e68cebf0becb18468467be5b40a1d64dc396d0 100644
--- a/LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeys-with-session.html
+++ b/LayoutTests/media/encrypted-media/encrypted-media-lifetime-mediakeys-with-session.html
@@ -38,17 +38,14 @@
                 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 promise.
-                    assert_equals(numActiveDOMObjectsCreated(), 1, 'MediaKeys.create()');
+                    // Verify MediaKeys are not an ActiveDOMObject.
+                    assert_equals(numActiveDOMObjectsCreated(), 0, 'MediaKeys.create()');
 
                     var initDataType = getInitDataType();
                     return mediaKeys.createSession(initDataType, getInitData(initDataType));
                 }).then(function(mediaKeySession) {
-                    // 1 MediaKeySession + 1 PromiseResolver.
-                    assert_equals(numActiveDOMObjectsCreated(), 2, 'MediaKeys.createSession()');
+                    // 1 MediaKeySession.
+                    assert_equals(numActiveDOMObjectsCreated(), 1, 'MediaKeys.createSession()');
 
                     // Run gc(), should not affect MediaKeys object nor the
                     // session since we still have a reference to it.