Fix atomic ops on ARM to compile in NaCl untrusted targets.

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 114 matching lines @@
 #endif  // ARCH_CPU_64_BITS
 
 }  // namespace base::subtle
 }  // namespace base
 
 // Include our platform specific implementation.
 #if defined(OS_WIN) && defined(COMPILER_MSVC) && defined(ARCH_CPU_X86_FAMILY)
 #include "base/atomicops_internals_x86_msvc.h"
 #elif defined(OS_MACOSX)
 #include "base/atomicops_internals_mac.h"
+#elif defined(OS_NACL)
+#include "base/atomicops_internals_nacl.h"
 #elif defined(COMPILER_GCC) && defined(ARCH_CPU_X86_FAMILY)
 #include "base/atomicops_internals_x86_gcc.h"
 #elif defined(COMPILER_GCC) && defined(ARCH_CPU_ARM_FAMILY)
 #include "base/atomicops_internals_arm_gcc.h"
 #elif defined(COMPILER_GCC) && defined(ARCH_CPU_MIPS_FAMILY)
 #include "base/atomicops_internals_mips_gcc.h"
 #else
 #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_