Implement PostDelayedTaskAt for guaranteed timer ordering

components/scheduler/renderer/null_renderer_scheduler.cc

Index: components/scheduler/renderer/null_renderer_scheduler.cc
diff --git a/components/scheduler/renderer/null_renderer_scheduler.cc b/components/scheduler/renderer/null_renderer_scheduler.cc
index e5052ad7068dc1c86ac31b4b210d986230dd41a0..96333acfece819689e87a6f679fa033aad12f8d2 100644
--- a/components/scheduler/renderer/null_renderer_scheduler.cc
+++ b/components/scheduler/renderer/null_renderer_scheduler.cc
@@ -8,19 +8,19 @@
 #include "base/message_loop/message_loop.h"
 #include "base/thread_task_runner_handle.h"
 #include "components/scheduler/child/null_idle_task_runner.h"
+#include "components/scheduler/child/null_task_queue.h"
 
 namespace scheduler {
 
 NullRendererScheduler::NullRendererScheduler()
-    : task_runner_(base::ThreadTaskRunnerHandle::Get()),
+    : task_runner_(new NullTaskQueue(base::ThreadTaskRunnerHandle::Get())),
       idle_task_runner_(new NullIdleTaskRunner()) {
 }
 
 NullRendererScheduler::~NullRendererScheduler() {
 }
 
-scoped_refptr<base::SingleThreadTaskRunner>
-NullRendererScheduler::DefaultTaskRunner() {
+scoped_refptr<TaskQueue> NullRendererScheduler::DefaultTaskRunner() {
   return task_runner_;
 }
 
@@ -39,8 +39,7 @@ NullRendererScheduler::IdleTaskRunner() {
   return idle_task_runner_;
 }
 
-scoped_refptr<base::SingleThreadTaskRunner>
-NullRendererScheduler::TimerTaskRunner() {
+scoped_refptr<TaskQueue> NullRendererScheduler::TimerTaskRunner() {
   return task_runner_;
 }