Second attempt at fixing warning on Windows.

runtime/vm/object.cc

 // 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.
 
 #include "vm/object.h"
 
 #include "include/dart_api.h"
 #include "platform/assert.h"
 #include "vm/assembler.h"
 #include "vm/cpu.h"
@@ skipping 16717 matching lines @@
 }
 
 
 uint32_t Bigint::AsTruncatedUint32Value() const {
   // Note: the previous implementation of Bigint returned the absolute value
   // truncated to 32 bits, which is not consistent with Smi and Mint behavior.
   ASSERT(Bigint::kBitsPerDigit == 32);
   const intptr_t used = Used();
   if (used == 0) return 0;
   const uint32_t digit0 = DigitAt(0);
-  return Neg() ? static_cast<uint32_t>(-digit0) : digit0;
+  return Neg() ? static_cast<uint32_t>(-static_cast<int32_t>(digit0)) : digit0;

[siva, 2014/10/01 00:04:40]

The multiple casts does look weird.

 }
 
 
 // For positive values: Smi < Mint < Bigint.
 int Bigint::CompareWith(const Integer& other) const {
   ASSERT(!FitsIntoSmi());
   ASSERT(!FitsIntoInt64());
   if (other.IsBigint() && (IsNegative() == other.IsNegative())) {
     const Bigint& other_bgi = Bigint::Cast(other);
     int64_t result = Used() - other_bgi.Used();
@@ skipping 3546 matching lines @@
   return tag_label.ToCString();
 }
 
 
 void UserTag::PrintJSONImpl(JSONStream* stream, bool ref) const {
   Instance::PrintJSONImpl(stream, ref);
 }
 
 
 }  // namespace dart