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

runtime/vm/dart_api_state.h

 // Copyright (c) 2012, 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_DART_API_STATE_H_
 #define VM_DART_API_STATE_H_
 
 #include "include/dart_api.h"
 
 #include "platform/utils.h"
@@ skipping 243 matching lines @@
 
  private:
   enum {
     kExternalNewSpaceBit = 0,
     kExternalSizeBits = 1,
     kExternalSizeBitsSize = (kBitsPerWord - 1),
   };
 
   // This part of external_data_ is the number of externally allocated bytes.
   // TODO(koda): Measure size in words instead.
-  class ExternalSizeBits : public BitField<intptr_t,
+  class ExternalSizeBits : public BitField<uword,
+                                           intptr_t,
                                            kExternalSizeBits,
-                                           kExternalSizeBitsSize> {};  // NOLINT
+                                           kExternalSizeBitsSize> {};
   // This bit of external_data_ is true if the referent was created in new
   // space and UpdateRelocated has not yet detected any promotion.
-  class ExternalNewSpaceBit : public BitField<bool, kExternalNewSpaceBit, 1> {};
+  class ExternalNewSpaceBit :
+      public BitField<uword, bool, kExternalNewSpaceBit, 1> {};
 
   friend class FinalizablePersistentHandles;
 
   FinalizablePersistentHandle()
       : raw_(NULL),
         peer_(NULL),
         external_data_(0),
         callback_(NULL) { }
   ~FinalizablePersistentHandle() { }
 
@@ skipping 488 matching lines @@
   ref->set_peer(peer);
   ref->set_callback(callback);
   // This may trigger GC, so it must be called last.
   ref->SetExternalSize(external_size, isolate);
   return ref;
 }
 
 }  // namespace dart
 
 #endif  // VM_DART_API_STATE_H_