Implement PostDelayedTaskAt for guaranteed timer ordering

components/scheduler/child/null_task_queue.cc

Index: components/scheduler/child/null_task_queue.cc
diff --git a/components/scheduler/child/null_task_queue.cc b/components/scheduler/child/null_task_queue.cc
new file mode 100644
index 0000000000000000000000000000000000000000..ef5bab5095e85cc7a334e33db19ecba69133eeb8
--- /dev/null
+++ b/components/scheduler/child/null_task_queue.cc
@@ -0,0 +1,41 @@
+// 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.
+
+#include "components/scheduler/child/null_task_queue.h"
+
+namespace scheduler {
+
+NullTaskQueue::NullTaskQueue(
+    scoped_refptr<base::SingleThreadTaskRunner> task_runner)
+    : task_runner_(task_runner) {}
+
+NullTaskQueue::~NullTaskQueue() {}
+
+bool NullTaskQueue::RunsTasksOnCurrentThread() const {
+  return task_runner_->RunsTasksOnCurrentThread();
+}
+
+bool NullTaskQueue::PostDelayedTask(const tracked_objects::Location& from_here,
+                                    const base::Closure& task,
+                                    base::TimeDelta delay) {
+  return task_runner_->PostDelayedTask(from_here, task, delay);
+}
+
+bool NullTaskQueue::PostNonNestableDelayedTask(
+    const tracked_objects::Location& from_here,
+    const base::Closure& task,
+    base::TimeDelta delay) {
+  return task_runner_->PostNonNestableDelayedTask(from_here, task, delay);
+}
+bool NullTaskQueue::PostDelayedTaskAt(
+    const tracked_objects::Location& from_here,
+    const base::Closure& task,
+    base::TimeTicks desired_run_time) {
+  // Note: this loses the guarantee of monotonicity but we can't do any better
+  // with base::TaskRunner.
+  return task_runner_->PostDelayedTask(
+      from_here, task, desired_run_time - base::TimeTicks::Now());
+}
+
+}  // namespace scheduler