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
 #
 # Since base includes so many low-level things that vary widely and
 # unpredictably for the various build types, we prefer a slightly different
 # style. Instead, there are big per-platform blocks of inclusions and
 # exclusions. If a given file has an inclusion or exclusion rule that applies
 # for multiple conditions, prefer to duplicate it in both lists. This makes it
 # a bit easier to see which files apply in which cases rather than having a
 # huge sequence of random-looking conditionals.
 
 import("//build/buildflag_header.gni")
 import("//build/config/allocator.gni")
+import("//build/config/arm.gni")
 import("//build/config/chromecast_build.gni")
 import("//build/config/clang/clang.gni")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/dcheck_always_on.gni")
 import("//build/config/nacl/config.gni")
 import("//build/config/sysroot.gni")
 import("//build/config/ui.gni")
 import("//build/nocompile.gni")
 import("//testing/libfuzzer/fuzzer_test.gni")
 import("//testing/test.gni")
@@ skipping 1176 matching lines @@
     # 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",
     ]
   }
 
+  # SpinLock uses inline assembly that doesn't work on NaCl, and for which there
+  # is no code for ARMv6.
+  if (!is_nacl && (current_cpu != "arm" || arm_version >= 7)) {
+    sources += [
+      "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",
     ]
 
     sources -= [
       "message_loop/message_pump_libevent.cc",
@@ skipping 1274 matching lines @@
 }
 
 fuzzer_test("base_json_correctness_fuzzer") {
   sources = [
     "json/correctness_fuzzer.cc",
   ]
   deps = [
     ":base",
   ]
 }