Workaround to make MemoryBarrier compile on Win x64

base/atomicops.h

 // Copyright (c) 2012 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.
 
 // For atomic operations on reference counts, see atomic_refcount.h.
 // For atomic operations on sequence numbers, see atomic_sequence_num.h.
 
 // The routines exported by this module are subtle.  If you use them, even if
 // you get the code right, it will depend on careful reasoning about atomicity
 // and memory ordering; it will be less readable, and harder to maintain.  If
@@ skipping 13 matching lines @@
 // Although there are currently no compiler enforcement, you are encouraged
 // to use these.
 //
 
 #ifndef BASE_ATOMICOPS_H_
 #define BASE_ATOMICOPS_H_
 
 #include "base/basictypes.h"
 #include "build/build_config.h"
 
+#if defined(OS_WIN) && defined(ARCH_CPU_64_BITS)
+// windows.h #defines this (only on x64). This causes problems because the
+// public API also uses MemoryBarrier at the public name for this fence. So, on
+// X64, undef it, and call its documented
+// (http://msdn.microsoft.com/en-us/library/windows/desktop/ms684208.aspx)
+// implementation directly.
+#undef MemoryBarrier
+#endif
+
 namespace base {
 namespace subtle {
 
 typedef int32 Atomic32;
 #ifdef ARCH_CPU_64_BITS
 // We need to be able to go between Atomic64 and AtomicWord implicitly.  This
 // means Atomic64 and AtomicWord should be the same type on 64-bit.
 #if defined(OS_NACL)
 // NaCl's intptr_t is not actually 64-bits on 64-bit!
 // http://code.google.com/p/nativeclient/issues/detail?id=1162
@@ skipping 101 matching lines @@
 #error "Atomic operations are not supported on your platform"
 #endif
 
 // On some platforms we need additional declarations to make
 // AtomicWord compatible with our other Atomic* types.
 #if defined(OS_MACOSX) || defined(OS_OPENBSD)
 #include "base/atomicops_internals_atomicword_compat.h"
 #endif
 
 #endif  // BASE_ATOMICOPS_H_