Implements optional parameter handling in MIPS vm.

runtime/vm/disassembler_mips.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/disassembler.h"
 
 #include "vm/globals.h"  // Needed here to get TARGET_ARCH_MIPS.
 #if defined(TARGET_ARCH_MIPS)
 #include "platform/assert.h"
 
@@ skipping 314 matching lines @@
       break;
     }
     case SRLV: {
       if (instr->SaField() == 0) {
         Format(instr, "srlv 'rd, 'rt, 'rs");
       } else {
         Unknown(instr);
       }
       break;
     }
-    case SUB: {
-      Format(instr, "sub 'rd, 'rs, 'rt");
-      break;
-    }
     case SUBU: {
       Format(instr, "subu 'rd, 'rs, 'rt");
       break;
     }
     case XOR: {
       Format(instr, "xor 'rd, 'rs, 'rt");
       break;
     }
     default: {
       Unknown(instr);
@@ skipping 194 matching lines @@
                                   pc);
     pc += instruction_length;
   }
 
   return;
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_MIPS