Fix build:

runtime/vm/assembler_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_ASSEMBLER_MIPS_H_
 #define VM_ASSEMBLER_MIPS_H_
 
 #ifndef VM_ASSEMBLER_H_
 #error Do not include assembler_mips.h directly; use assembler.h instead.
 #endif
@@ skipping 140 matching lines @@
     kLeftPos = 0,
     kLeftSize = 6,
     kRightPos = kLeftPos + kLeftSize,
     kRightSize = 6,
     kRelOpPos = kRightPos + kRightSize,
     kRelOpSize = 4,
     kImmPos = kRelOpPos + kRelOpSize,
     kImmSize = 16,
   };
 
-  class LeftBits : public BitField<Register, kLeftPos, kLeftSize> {};
-  class RightBits : public BitField<Register, kRightPos, kRightSize> {};
-  class RelOpBits : public BitField<RelationOperator, kRelOpPos, kRelOpSize> {};
-  class ImmBits : public BitField<uint16_t, kImmPos, kImmSize> {};
+  class LeftBits : public BitField<uword, Register, kLeftPos, kLeftSize> {};
+  class RightBits : public BitField<uword, Register, kRightPos, kRightSize> {};
+  class RelOpBits :
+      public BitField<uword, RelationOperator, kRelOpPos, kRelOpSize> {};
+  class ImmBits : public BitField<uword, uint16_t, kImmPos, kImmSize> {};
 
   Register left() const { return LeftBits::decode(bits_); }
   Register right() const { return RightBits::decode(bits_); }
   RelationOperator rel_op() const { return RelOpBits::decode(bits_); }
   int16_t imm() const { return static_cast<int16_t>(ImmBits::decode(bits_)); }
 
   static bool IsValidImm(int32_t value) {
     // We want both value and value + 1 to fit in an int16_t.
     return (-0x08000 <= value) && (value < 0x7fff);
   }
@@ skipping 1576 matching lines @@
                                   Register value,
                                   Label* no_update);
 
   DISALLOW_ALLOCATION();
   DISALLOW_COPY_AND_ASSIGN(Assembler);
 };
 
 }  // namespace dart
 
 #endif  // VM_ASSEMBLER_MIPS_H_