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..8e41215ecf8e4278b6608c628da0dc238c9054b9 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 +92,12 @@ 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_ == NULL && thread_id_ == 0);

[danakj, 2014/10/16 17:14:59]

these are 2 DCHECKs, split them up (or isn't checking thread_id enough?)

also, DCHECK_EQ

[Avi (use Gerrit), 2014/10/16 18:02:55]

Yep. Two DCHECK_EQs, and nullptr.

[petrcermak, 2014/10/17 15:43:15]

Done. I kept both checks since thread_id is set only after the task is posted.

+  task_runner_ = task_runner;

[danakj, 2014/10/16 17:14:59]

task_runner has a reference already, swap it into place so you don't add another
reference here just to drop it

[petrcermak, 2014/10/17 15:43:15]

Done.

+}
+
 void Timer::Start(const tracked_objects::Location& posted_from,
                   TimeDelta delay,
                   const base::Closure& user_task) {
@@ -146,12 +151,12 @@ 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 +166,13 @@ void Timer::PostNewScheduledTask(TimeDelta delay) {
     thread_id_ = static_cast<int>(PlatformThread::CurrentId());
 }
 
+scoped_refptr<SingleThreadTaskRunner> Timer::GetTaskRunner() {
+  if (task_runner_.get() == NULL) {

[Avi (use Gerrit), 2014/10/16 18:02:55]

nullptr?

[petrcermak, 2014/10/17 15:43:15]

Done.

+    task_runner_ = ThreadTaskRunnerHandle::Get();

[danakj, 2014/10/16 17:14:59]

This will make Timer hold a ref on the current task runner when it did not do so
before. Let's not do that.

Instead just grab the current one in PostNewScheduledTask when task_runner_ is
null and use that instead of task_runner_.

[petrcermak, 2014/10/17 15:43:15]

Done. I did this initially but I was told to store the ref on the current task
runner.

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