Move WTF::SpinLock to base::SpinLock.

base/BUILD.gn

 # Copyright (c) 2013 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.
 
 # HOW TO WRITE CONDITIONALS IN THIS FILE
 # ======================================
 #
 # In many other places, one would write a conditional that expresses all the
 # cases when a source file is used or unused, and then either add or subtract
 # it from the sources list in that case
@@ skipping 682 matching lines @@
     "sequence_checker_impl.cc",
     "sequence_checker_impl.h",
     "sequence_token.cc",
     "sequence_token.h",
     "sequenced_task_runner.cc",
     "sequenced_task_runner.h",
     "sequenced_task_runner_helpers.h",
     "sha1.cc",
     "sha1.h",
     "single_thread_task_runner.h",
+    "spin_lock.cc",
+    "spin_lock.h",
     "stl_util.h",
     "strings/latin1_string_conversions.cc",
     "strings/latin1_string_conversions.h",
     "strings/nullable_string16.cc",
     "strings/nullable_string16.h",
     "strings/pattern.cc",
     "strings/pattern.h",
     "strings/safe_sprintf.cc",
     "strings/safe_sprintf.h",
     "strings/string16.cc",
@@ skipping 1756 matching lines @@
 }
 
 fuzzer_test("base_json_correctness_fuzzer") {
   sources = [
     "json/correctness_fuzzer.cc",
   ]
   deps = [
     ":base",
   ]
 }