Add testRunner.runIdleTasks() to force idle tasks to run.

components/scheduler/BUILD.gn

 # Copyright 2015 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 # GYP version: components/scheduler.gypi:scheduler
 component("scheduler") {
   sources = [
     "base/cancelable_closure_holder.cc",
     "base/cancelable_closure_holder.h",
     "base/enqueue_order.cc",
@@ skipping 145 matching lines @@
   ]
 }
 
 # GYP version: components/scheduler.gypi:scheduler_test_support
 source_set("test_support") {
   testonly = true
 
   sources = [
     "test/lazy_scheduler_message_loop_delegate_for_tests.cc",
     "test/lazy_scheduler_message_loop_delegate_for_tests.h",
+    "test/renderer_scheduler_test_support.cc",
+    "test/renderer_scheduler_test_support.h",
+  ]
+
+  deps = [
+    "//third_party/WebKit/public:blink",
   ]
 
   public_deps = [
     ":scheduler",
     "//base",
   ]
 }