A64: Synchronize with r16849.

src/a64/cpu-a64.h

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 62 matching lines @@
   static uint32_t GetCacheType();
 
   // I and D cache line size in bytes.
   static unsigned icache_line_size_;
   static unsigned dcache_line_size_;
 
 #ifdef DEBUG
   static bool initialized_;
 #endif
 
+  // This isn't used (and is always 0), but it is required by V8.
+  static unsigned found_by_runtime_probing_only_;
+
+  friend class PlatformFeatureScope;
   DISALLOW_COPY_AND_ASSIGN(CpuFeatures);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_A64_CPU_A64_H_