Revert of 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 1189 matching lines @@
     }
   } else {
     # Remove NaCl stuff.
     sources -= [
       "memory/shared_memory_nacl.cc",
       "os_compat_nacl.cc",
       "os_compat_nacl.h",
       "rand_util_nacl.cc",
       "synchronization/read_write_lock_nacl.cc",
     ]
-
-    # Add stuff that doesn't work in NaCl.
-    sources += [
-      # SpinLock uses GNU-style inline assembly, which the pnacl-clang++
-      # compiler doesn't allow.
-      "synchronization/spin_lock.cc",
-      "synchronization/spin_lock.h",
-    ]
   }
 
   # Windows.
   if (is_win) {
     sources += [
       "power_monitor/power_monitor_device_source_win.cc",
       "profiler/win32_stack_frame_unwinder.cc",
       "profiler/win32_stack_frame_unwinder.h",
     ]
 
@@ skipping 1270 matching lines @@
 }
 
 fuzzer_test("base_json_correctness_fuzzer") {
   sources = [
     "json/correctness_fuzzer.cc",
   ]
   deps = [
     ":base",
   ]
 }