Add a mechanism to override the detected cpu features.

src/ia32/assembler-ia32.cc

 // 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 33 matching lines @@
 
 namespace v8 {
 namespace internal {
 
 // -----------------------------------------------------------------------------
 // Implementation of CpuFeatures
 
 #ifdef DEBUG
 bool CpuFeatures::initialized_ = false;
 #endif
+uint64_t CpuFeatures::force_feature_ = 0;
 uint64_t CpuFeatures::supported_ = 0;
 uint64_t CpuFeatures::found_by_runtime_probing_only_ = 0;
 
 
 ExternalReference ExternalReference::cpu_features() {
   ASSERT(CpuFeatures::initialized_);
   return ExternalReference(&CpuFeatures::supported_);
 }
 
 
@@ skipping 2608 matching lines @@
     fprintf(coverage_log, "%s\n", file_line);
     fflush(coverage_log);
   }
 }
 
 #endif
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_IA32