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

content/test/layouttest_support.cc

 // Copyright (c) 2012 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 "content/public/test/layouttest_support.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/callback.h"
 #include "base/lazy_instance.h"
 #include "base/strings/string_util.h"
 #include "build/build_config.h"
+#include "components/scheduler/test/renderer_scheduler_test_support.h"
 #include "components/test_runner/test_common.h"
 #include "components/test_runner/web_frame_test_proxy.h"
 #include "components/test_runner/web_test_proxy.h"
 #include "content/browser/bluetooth/bluetooth_dispatcher_host.h"
 #include "content/browser/renderer_host/render_process_host_impl.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/child/geofencing/web_geofencing_provider_impl.h"
 #include "content/common/gpu/image_transport_surface.h"
 #include "content/common/site_isolation_policy.h"
 #include "content/public/common/page_state.h"
@@ skipping 423 matching lines @@
         PageStateToHistoryEntry(page_state[index]));
     result.append(
         DumpHistoryItem(entry->root_history_node(),
                         8,
                         index == current_index));
   }
   result.append("===============================================\n");
   return result;
 }
 
+void SchedulerRunIdleTasks(const base::Closure& callback) {
+    scheduler::RendererScheduler* scheduler =
+        content::RenderThreadImpl::current()->GetRendererScheduler();
+    scheduler::RunIdleTasksForTesting(scheduler, callback);
+}
+
 }  // namespace content