Fix unsigned multiplication in MIPS simulator (add assembler regression test).

runtime/vm/constants_mips.h

 // 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.
 
 #ifndef VM_CONSTANTS_MIPS_H_
 #define VM_CONSTANTS_MIPS_H_
 
 #include "platform/assert.h"
 
 namespace dart {
@@ skipping 438 matching lines @@
   FMT_PS = 22,
 };
 
 
 class Instr {
  public:
   enum {
     kInstrSize = 4,
   };
 
+  static const int32_t kNopInstruction = 0;
+
+  // Reserved break instruction codes.
+  static const int32_t kStopMessageCode = 1 << 16;  // For Stop(message).
+  static const int32_t kRedirectCode = 2 << 16;  // For call redirection in sim.
+  static const int32_t kMsgMessageCode = 3 << 16;  // For trace message in sim.
+  static const int32_t kSimulatorBreakCode = 4 << 16;  // For breakpoint in sim.
+
+  // General breakpoint instruction: break(0), for user breakpoint and to fill
+  // assembler code buffers in debug mode.
   static const int32_t kBreakPointInstruction =
       (SPECIAL << kOpcodeShift) | (BREAK << kFunctionShift);
-  static const int32_t kNopInstruction = 0;
-  static const int32_t kStopMessageCode = 1;
-  static const int32_t kRedirectCode = 2;
-  static const int32_t kMsgMessageCode = 3;
 
   // Get the raw instruction bits.
   inline int32_t InstructionBits() const {
     return *reinterpret_cast<const int32_t*>(this);
   }
 
   // Set the raw instruction bits to value.
   inline void SetInstructionBits(int32_t value) {
     *reinterpret_cast<int32_t*>(this) = value;
   }
@@ skipping 139 matching lines @@
 #endif  // defined(DEBUG)
 
  private:
   DISALLOW_ALLOCATION();
   DISALLOW_IMPLICIT_CONSTRUCTORS(Instr);
 };
 
 }  // namespace dart
 
 #endif  // VM_CONSTANTS_MIPS_H_