Revert of Move WTF::SpinLock to base::SpinLock.

third_party/WebKit/Source/wtf/BUILD.gn

 # 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.
 
 assert(!is_ios)
 
 import("//testing/test.gni")
 import("//third_party/WebKit/Source/config.gni")
 
 visibility = [
@@ skipping 92 matching lines @@
     "PassRefPtr.h",
     "PrintStream.cpp",
     "PrintStream.h",
     "PtrUtil.h",
     "RefCounted.h",
     "RefPtr.h",
     "RetainPtr.h",
     "SaturatedArithmetic.h",
     "SizeAssertions.h",
     "SizeLimits.cpp",
+    "SpinLock.cpp",
     "SpinLock.h",
     "StaticConstructors.h",
     "StdLibExtras.h",
     "StringExtras.h",
     "StringHasher.h",
     "ThreadRestrictionVerifier.h",
     "ThreadSafeRefCounted.h",
     "ThreadSpecific.h",
     "ThreadSpecificWin.cpp",
     "Threading.h",
@@ skipping 232 matching lines @@
   configs += [ "//third_party/WebKit/Source:config" ]
 
   deps = [
     ":wtf",
     "//base",
     "//base/test:test_support",
     "//testing/gmock",
     "//testing/gtest",
   ]
 }