Fix some more shorten-64-to-32 warnings:

runtime/vm/locations.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_LOCATIONS_H_
 #define VM_LOCATIONS_H_
 
 #include "vm/allocation.h"
 #include "vm/assembler.h"
 #include "vm/bitfield.h"
@@ skipping 369 matching lines @@
  private:
   explicit Location(uword value) : value_(value) { }
 
   Location(Kind kind, uword payload)
       : value_(KindField::encode(kind) | PayloadField::encode(payload)) { }
 
   uword payload() const {
     return PayloadField::decode(value_);
   }
 
-  typedef BitField<Kind, 0, kBitsForKind> KindField;
-  typedef BitField<uword, kBitsForKind, kBitsForPayload> PayloadField;
+  class KindField : public BitField<uword, Kind, 0, kBitsForKind> {};
+  class PayloadField :
+      public BitField<uword, uword, kBitsForKind, kBitsForPayload> {};
 
   // Layout for kUnallocated locations payload.
-  typedef BitField<Policy, 0, 3> PolicyField;
+  typedef BitField<uword, Policy, 0, 3> PolicyField;
 
   // Layout for stack slots.
   static const intptr_t kBitsForBaseReg = 5;
   static const intptr_t kBitsForStackIndex = kBitsForPayload - kBitsForBaseReg;
-  typedef BitField<Register, 0, kBitsForBaseReg> StackSlotBaseField;
-  typedef BitField<intptr_t,
-                   kBitsForBaseReg,
-                   kBitsForStackIndex> StackIndexField;
+  class StackSlotBaseField :
+      public BitField<uword, Register, 0, kBitsForBaseReg> {};
+  class StackIndexField :
+      public BitField<uword, intptr_t, kBitsForBaseReg, kBitsForStackIndex> {};
   COMPILE_ASSERT(1 << kBitsForBaseReg >= kNumberOfCpuRegisters);
 
   static const intptr_t kStackIndexBias =
       static_cast<intptr_t>(1) << (kBitsForStackIndex - 1);
 
   // Location either contains kind and payload fields or a tagged handle for
   // a constant locations. Values of enumeration Kind are selected in such a
   // way that none of them can be interpreted as a kConstant tag.
   uword value_;
 };
@@ skipping 296 matching lines @@
 
 #if defined(DEBUG)
   intptr_t writable_inputs_;
 #endif
 };
 
 
 }  // namespace dart
 
 #endif  // VM_LOCATIONS_H_