(reland) Adds TimeDomains to the TaskQueueManager

components/scheduler/base/test_time_source.cc

 // 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/base/test_time_source.h"
 
 namespace scheduler {
 
 TestTimeSource::TestTimeSource(base::SimpleTestTickClock* time_source)
-    : time_source_(time_source) {}
+    : time_source_(time_source) {
+  DCHECK(time_source_);
+}
 
 TestTimeSource::~TestTimeSource() {}
 
 base::TimeTicks TestTimeSource::NowTicks() {
   return time_source_->NowTicks();
 }
 
 }  // namespace scheduler