Add a mechanism to override the detected cpu features.

src/mips/assembler-mips.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 408 matching lines @@
   }
 
  private:
 #ifdef DEBUG
   static bool initialized_;
 #endif
   static unsigned supported_;
   static unsigned found_by_runtime_probing_only_;
 
   friend class ExternalReference;
+  friend class PlatformFeatureScope;
   DISALLOW_COPY_AND_ASSIGN(CpuFeatures);
 };
 
 
 class Assembler : public AssemblerBase {
  public:
   // Create an assembler. Instructions and relocation information are emitted
   // into a buffer, with the instructions starting from the beginning and the
   // relocation information starting from the end of the buffer. See CodeDesc
   // for a detailed comment on the layout (globals.h).
@@ skipping 771 matching lines @@
 class EnsureSpace BASE_EMBEDDED {
  public:
   explicit EnsureSpace(Assembler* assembler) {
     assembler->CheckBuffer();
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_ARM_ASSEMBLER_MIPS_H_