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

Note to crash team: This CL is a refactor and has no intended behavior change.

This change was scripted by https://crbug.com/676387#c8.

Note-worthy for the reviewer:
 * SequenceChecker enforces thread-safety but not thread-affinity!
   If the classes that were updated are thread-affine (use thread local
   storage or a third-party API that does) they should be migrated to
   ThreadChecker instead.
 * ~NonThreadSafe() used to implcitly check in its destructor
   ~Sequence/ThreadChecker() doesn't by design. To keep this CL a
   no-op, an explicit check was added to the destructor of migrated
   classes.
 * NonThreadSafe used to provide access to subclasses, as such
   the |sequence_checker_| member was made protected rather than
   private where necessary.

BUG=676387
This CL was uploaded by git cl split.

[email protected]

Review-Url: https://codereview.chromium.org/2907303002
Cr-Commit-Position: refs/heads/master@{#476274}
diff --git a/base/deferred_sequenced_task_runner_unittest.cc b/base/deferred_sequenced_task_runner_unittest.cc
index 799ddcd..a96befa 100644
--- a/base/deferred_sequenced_task_runner_unittest.cc
+++ b/base/deferred_sequenced_task_runner_unittest.cc
@@ -11,15 +11,13 @@
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
-#include "base/threading/non_thread_safe.h"
 #include "base/threading/thread.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
 
-class DeferredSequencedTaskRunnerTest : public testing::Test,
-                                        public base::NonThreadSafe {
+class DeferredSequencedTaskRunnerTest : public testing::Test {
  public:
   class ExecuteTaskOnDestructor :
       public base::RefCounted<ExecuteTaskOnDestructor> {