Support dec_b instruction in ia32 and x64 disassembler.

test/cctest/test-disasm-ia32.cc

 // Copyright 2007-2008 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 147 matching lines @@
   __ movsx_b(edx, Operand(esp, 12));
   __ movzx_w(edx, Operand(esp, 12));
   __ movzx_b(edx, Operand(esp, 12));
   __ nop();
   __ mov(edx, 1234567);
   __ mov(edx, Operand(esp, 12));
   __ mov(Operand(ebx, ecx, times_4, 10000), Immediate(12345));
   __ mov(Operand(ebx, ecx, times_4, 10000), edx);
   __ nop();
   __ dec_b(edx);
+  __ dec_b(Operand(eax, 10));
+  __ dec_b(Operand(ebx, ecx, times_4, 10000));
   __ dec(edx);
   __ cdq();
 
   __ nop();
   __ idiv(edx);
   __ mul(edx);
   __ neg(edx);
   __ not_(edx);
   __ test(Operand(ebx, ecx, times_4, 10000), Immediate(123456));
 
@@ skipping 262 matching lines @@
   CHECK(code->IsCode());
 #ifdef DEBUG
   Code::cast(code)->Print();
   byte* begin = Code::cast(code)->instruction_start();
   byte* end = begin + Code::cast(code)->instruction_size();
   disasm::Disassembler::Disassemble(stdout, begin, end);
 #endif
 }
 
 #undef __