Fix unused variable warning in the Win-Clang build

base/allocator/allocator_shim.cc

 // Copyright 2016 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.
 
 #include "base/allocator/allocator_shim.h"
 
 #include <errno.h>
 
 #include <new>
 
@@ skipping 16 matching lines @@
 // they are safe to use today, in future they might be refactored.
 
 namespace {
 
 using namespace base;
 
 subtle::AtomicWord g_chain_head = reinterpret_cast<subtle::AtomicWord>(
     &allocator::AllocatorDispatch::default_dispatch);
 
 bool g_call_new_handler_on_malloc_failure = false;
+
+#if !defined(OS_WIN)
 subtle::Atomic32 g_new_handler_lock = 0;
+#endif
 
 // In theory this should be just base::ThreadChecker. But we can't afford
 // the luxury of a LazyInstance<ThreadChecker> here as it would cause a new().
 bool CalledOnValidThread() {
   using subtle::Atomic32;
   const Atomic32 kInvalidTID = static_cast<Atomic32>(kInvalidThreadId);
   static Atomic32 g_tid = kInvalidTID;
   Atomic32 cur_tid = static_cast<Atomic32>(PlatformThread::CurrentId());
   Atomic32 prev_tid =
       subtle::NoBarrier_CompareAndSwap(&g_tid, kInvalidTID, cur_tid);
@@ skipping 222 matching lines @@
 // Cross-checks.
 
 #if defined(MEMORY_TOOL_REPLACES_ALLOCATOR)
 #error The allocator shim should not be compiled when building for memory tools.
 #endif
 
 #if (defined(__GNUC__) && defined(__EXCEPTIONS)) || \
     (defined(_HAS_EXCEPTIONS) && _HAS_EXCEPTIONS)
 #error This code cannot be used when exceptions are turned on.
 #endif