[scheduler] Moving SetTimerSlack API from MessageLoop to SequenceManager.

In preparation for removing MessageLoop, we are making ThreadMain invoke SetTimerSlack on the SequenceManager as well as the MessageLoop.

Bug: 891670
Change-Id: I5e4fc8af654a62d543e3965603ee15c206a31d93
Reviewed-on: https://chromium-review.googlesource.com/c/1310433Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: danakj <danakj@chromium.org>
Commit-Queue: Karolina Soltys <ksolt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605702}

base/threading/thread.cc

@@ -97,7 +97,7 @@ bool Thread::StartWithOptions(const Options& options) {
   if (!options.message_pump_factory.is_null())
     type = MessageLoop::TYPE_CUSTOM;
 
-  message_loop_timer_slack_ = options.timer_slack;
+  timer_slack_ = options.timer_slack;
   std::unique_ptr<MessageLoop> message_loop_owned =
       MessageLoop::CreateUnbound(type, options.message_pump_factory);
   message_loop_ = message_loop_owned.get();
@@ -313,9 +313,10 @@ void Thread::ThreadMain() {
   DCHECK(message_loop_);
   std::unique_ptr<MessageLoop> message_loop(message_loop_);
   message_loop_->BindToCurrentThread();
-  message_loop_->SetTimerSlack(message_loop_timer_slack_);
+  message_loop_->SetTimerSlack(timer_slack_);
 
   if (sequence_manager_) {
+    sequence_manager_->SetTimerSlack(timer_slack_);
     sequence_manager_->CompleteInitializationOnBoundThread();
   }
 

base/threading/thread.h

@@ -344,9 +344,9 @@ class BASE_EXPORT Thread : PlatformThread::Delegate {
   // Optionally stores a SequenceManager that manages Tasks on the MessageLoop.
   std::unique_ptr<sequence_manager::SequenceManager> sequence_manager_;
 
-  // Stores Options::timer_slack_ until the message loop has been bound to
+  // Stores Options::timer_slack_ until the sequence manager has been bound to
   // a thread.
-  TimerSlack message_loop_timer_slack_ = TIMER_SLACK_NONE;
+  TimerSlack timer_slack_ = TIMER_SLACK_NONE;
 
   // The name of the thread.  Used for debugging purposes.
   const std::string name_;