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

components/scheduler/test/renderer_scheduler_test_support.cc

+// Copyright 2016 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.
+
+#include "components/scheduler/test/renderer_scheduler_test_support.h"
+
+#include "components/scheduler/renderer/renderer_scheduler_impl.h"
+
+namespace scheduler {
+
+void RunIdleTasksForTesting(
+    RendererScheduler* scheduler,
+    const base::Closure& callback) {
+  RendererSchedulerImpl* scheduler_impl = static_cast<RendererSchedulerImpl*>(
+      scheduler);
+  scheduler_impl->RunIdleTasksForTesting(callback);
+}
+
+} // namespace scheduler