Modernize TimerTests prior to https://codereview.chromium.org/2491613004

base/timer/timer.cc

Index: base/timer/timer.cc
diff --git a/base/timer/timer.cc b/base/timer/timer.cc
index aba8fc8d9fbca7d6c22097c7c5230d682733469f..6ec18f181488c3a5b533abe93cf9b793914e6451 100644
--- a/base/timer/timer.cc
+++ b/base/timer/timer.cc
@@ -181,10 +181,8 @@ void Timer::PostNewScheduledTask(TimeDelta delay) {
   }
   // Remember the thread ID that posts the first task -- this will be verified
   // later when the task is abandoned to detect misuse from multiple threads.
-  if (!thread_id_) {
-    DCHECK(GetTaskRunner()->BelongsToCurrentThread());
+  if (!thread_id_)
     thread_id_ = static_cast<int>(PlatformThread::CurrentId());
-  }
 }
 
 scoped_refptr<SingleThreadTaskRunner> Timer::GetTaskRunner() {