Fix/implement new write barrier for x64.

src/ia32/assembler-ia32.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 72 matching lines @@
       "eax",
       "ecx",
       "edx",
       "ebx",
       "edi"
     };
     return names[index];
   }
 
   static Register from_code(int code) {
+    ASSERT(code >= 0);
+    ASSERT(code < kNumRegisters);
     Register r = { code };
     return r;
   }
   bool is_valid() const { return 0 <= code_ && code_ < kNumRegisters; }
   bool is(Register reg) const { return code_ == reg.code_; }
   // eax, ebx, ecx and edx are byte registers, the rest are not.
   bool is_byte_register() const { return code_ <= 3; }
   int code() const {
     ASSERT(is_valid());
     return code_;
@@ skipping 973 matching lines @@
  private:
   Assembler* assembler_;
 #ifdef DEBUG
   int space_before_;
 #endif
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_IA32_ASSEMBLER_IA32_H_