Replace deprecated base::NonThreadSafe in /cc in favor of SequenceChecker.

cc/test/fake_external_begin_frame_source.cc

Index: cc/test/fake_external_begin_frame_source.cc
diff --git a/cc/test/fake_external_begin_frame_source.cc b/cc/test/fake_external_begin_frame_source.cc
index 8398dcfc16c07f4f814513db2fc5cf63319bb67f..a2a0b3d5ab451f2f36d0b5e5c646f87e828ca029 100644
--- a/cc/test/fake_external_begin_frame_source.cc
+++ b/cc/test/fake_external_begin_frame_source.cc
@@ -18,11 +18,11 @@ FakeExternalBeginFrameSource::FakeExternalBeginFrameSource(
     : tick_automatically_(tick_automatically),
       milliseconds_per_frame_(1000.0 / refresh_rate),
       weak_ptr_factory_(this) {
-  DetachFromThread();
+  DETACH_FROM_SEQUENCE(sequence_checker_);
 }
 
 FakeExternalBeginFrameSource::~FakeExternalBeginFrameSource() {
-  DCHECK(CalledOnValidThread());
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
 }
 
 void FakeExternalBeginFrameSource::SetPaused(bool paused) {
@@ -87,7 +87,7 @@ BeginFrameArgs FakeExternalBeginFrameSource::CreateBeginFrameArgs(
 
 void FakeExternalBeginFrameSource::TestOnBeginFrame(
     const BeginFrameArgs& args) {
-  DCHECK(CalledOnValidThread());
+  DCHECK_CALLED_ON_VALID_SEQUENCE(sequence_checker_);
   current_args_ = args;
   std::set<BeginFrameObserver*> observers(observers_);
   for (auto* obs : observers)