Add support to base::Timer for custom task runners.

base/timer/timer.cc

Index: base/timer/timer.cc
diff --git a/base/timer/timer.cc b/base/timer/timer.cc
index 1916ccc34ebb7c7bf328533ba8911ddd11679b17..ea6f884a223bf0c0e95e5eb78841d304c42b6404 100644
--- a/base/timer/timer.cc
+++ b/base/timer/timer.cc
@@ -8,7 +8,6 @@
 
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
-#include "base/single_thread_task_runner.h"
 #include "base/thread_task_runner_handle.h"
 #include "base/threading/platform_thread.h"
 
@@ -93,6 +92,13 @@ TimeDelta Timer::GetCurrentDelay() const {
   return delay_;
 }
 
+void Timer::SetTaskRunner(scoped_refptr<SingleThreadTaskRunner> task_runner) {
+  // Do not allow changing the task runner once something has been scheduled.
+  DCHECK(scheduled_task_ == nullptr);

[danakj, 2014/10/18 19:00:00]

use DCHECK_EQ

i still don't understand what this is adding over the thread_id_ check. are you
worrying about this being called in the same stack frame from
PostNewScheduledTask? I don't think that's possible since the task is posted,
and it would get a new stack frame, and the thread_id_ would be set by then?

[petrcermak, 2014/10/20 12:42:41]

I originally added it to check that no other thread modifies the task runner
while the first task is being scheduled. I removed it now.

+  DCHECK(thread_id_ == 0);

[danakj, 2014/10/18 19:00:00]

use DCHECK_EQ

[petrcermak, 2014/10/20 12:42:41]

Done.

+  task_runner_.swap(task_runner);
+}
+
 void Timer::Start(const tracked_objects::Location& posted_from,
                   TimeDelta delay,
                   const base::Closure& user_task) {
@@ -146,12 +152,12 @@ void Timer::PostNewScheduledTask(TimeDelta delay) {
   is_running_ = true;
   scheduled_task_ = new BaseTimerTaskInternal(this);
   if (delay > TimeDelta::FromMicroseconds(0)) {
-    ThreadTaskRunnerHandle::Get()->PostDelayedTask(posted_from_,
+    GetTaskRunner()->PostDelayedTask(posted_from_,
         base::Bind(&BaseTimerTaskInternal::Run, base::Owned(scheduled_task_)),
         delay);
     scheduled_run_time_ = desired_run_time_ = TimeTicks::Now() + delay;
   } else {
-    ThreadTaskRunnerHandle::Get()->PostTask(posted_from_,
+    GetTaskRunner()->PostTask(posted_from_,
         base::Bind(&BaseTimerTaskInternal::Run, base::Owned(scheduled_task_)));
     scheduled_run_time_ = desired_run_time_ = TimeTicks();
   }
@@ -161,6 +167,11 @@ void Timer::PostNewScheduledTask(TimeDelta delay) {
     thread_id_ = static_cast<int>(PlatformThread::CurrentId());
 }
 
+scoped_refptr<SingleThreadTaskRunner> Timer::GetTaskRunner() {
+  return task_runner_.get() == nullptr ?

[danakj, 2014/10/18 19:00:00]

== nullptr is redundant here

return task_runner_.get() ? task_runner_ : RunnerHandle::Get() ?

[petrcermak, 2014/10/20 12:42:41]

Done.

+      ThreadTaskRunnerHandle::Get() : task_runner_;
+}
+
 void Timer::AbandonScheduledTask() {
   DCHECK(thread_id_ == 0 ||
          thread_id_ == static_cast<int>(PlatformThread::CurrentId()));