Workaround to make MemoryBarrier compile on Win x64

base/atomicops.h

Index: base/atomicops.h
diff --git a/base/atomicops.h b/base/atomicops.h
index de5554ebb9bea28c529e0ef38050320b69b4367d..13fb7e412ded1e0abbde87362b52c8900d58bc42 100644
--- a/base/atomicops.h
+++ b/base/atomicops.h
@@ -31,6 +31,15 @@
 #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 {