Fix the types used in bit fields.

vm/snapshot.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_SNAPSHOT_H_
 #define VM_SNAPSHOT_H_
 
 #include "platform/assert.h"
 #include "vm/allocation.h"
 #include "vm/bitfield.h"
@@ skipping 147 matching lines @@
   // sizeof(T) must be in {1,2,4,8}.
   template <typename T>
   T Read() {
     return ReadStream::Raw<sizeof(T), T>::Read(&stream_);
   }
 
   // Reads an intptr_t type value.
   intptr_t ReadIntptrValue() {
     int64_t value = Read<int64_t>();
     ASSERT((value <= kIntptrMax) && (value >= kIntptrMin));
-    return value;
+    return static_cast<intptr_t>(value);
   }
 
   void ReadBytes(uint8_t* addr, intptr_t len) {
     stream_.ReadBytes(addr, len);
   }
 
   const uint8_t* CurrentBufferAddress() const {
     return stream_.AddressOfCurrentPosition();
   }
 
@@ skipping 391 matching lines @@
  private:
   SnapshotWriter* writer_;
   bool as_references_;
 
   DISALLOW_COPY_AND_ASSIGN(SnapshotWriterVisitor);
 };
 
 }  // namespace dart
 
 #endif  // VM_SNAPSHOT_H_