Add a mechanism to override the detected cpu features.

src/arm/assembler-arm.h

 // Copyright (c) 1994-2006 Sun Microsystems Inc.
 // 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.
 //
@@ skipping 71 matching lines @@
 
  private:
 #ifdef DEBUG
   static bool initialized_;
 #endif
   static unsigned supported_;
   static unsigned found_by_runtime_probing_only_;
   static unsigned cache_line_size_;
 
   friend class ExternalReference;
+  friend class PlatformFeatureScope;
   DISALLOW_COPY_AND_ASSIGN(CpuFeatures);
 };
 
 
 // CPU Registers.
 //
 // 1) We would prefer to use an enum, but enum values are assignment-
 // compatible with int, which has caused code-generation bugs.
 //
 // 2) We would prefer to use a class instead of a struct but we don't like
@@ skipping 1473 matching lines @@
  public:
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_ASSEMBLER_ARM_H_