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

cc/test/fake_external_begin_frame_source.h

 // Copyright 2014 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.
 
 #ifndef CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_
 #define CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_
 
 #include <set>
 
 #include "base/cancelable_callback.h"
 #include "base/memory/weak_ptr.h"
-#include "base/threading/non_thread_safe.h"
+#include "base/sequence_checker.h"
 #include "cc/output/begin_frame_args.h"
 #include "cc/scheduler/begin_frame_source.h"
 
 namespace base {
 class SimpleTestTickClock;
 }  // namespace base
 
 namespace cc {
 
-class FakeExternalBeginFrameSource
-    : public BeginFrameSource,
-      public NON_EXPORTED_BASE(base::NonThreadSafe) {
+class FakeExternalBeginFrameSource : public BeginFrameSource {
  public:
   class Client {
    public:
     virtual void OnAddObserver(BeginFrameObserver* obs) = 0;
     virtual void OnRemoveObserver(BeginFrameObserver* obs) = 0;
   };
 
   explicit FakeExternalBeginFrameSource(double refresh_rate,
                                         bool tick_automatically);
   ~FakeExternalBeginFrameSource() override;
@@ skipping 21 matching lines @@
   void PostTestOnBeginFrame();
 
   const bool tick_automatically_;
   const double milliseconds_per_frame_;
   Client* client_ = nullptr;
   bool paused_ = false;
   BeginFrameArgs current_args_;
   uint64_t next_begin_frame_number_ = BeginFrameArgs::kStartingFrameNumber;
   std::set<BeginFrameObserver*> observers_;
   base::CancelableCallback<void(const BeginFrameArgs&)> begin_frame_task_;
+
+  SEQUENCE_CHECKER(sequence_checker_);
+
   base::WeakPtrFactory<FakeExternalBeginFrameSource> weak_ptr_factory_;
 };
 
 }  // namespace cc
 
 #endif  // CC_TEST_FAKE_EXTERNAL_BEGIN_FRAME_SOURCE_H_