Cleanups: addressed your comments from https://codereview.chromium.org/14962008/

runtime/lib/integers.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/bootstrap_natives.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/dart_entry.h"
 #include "vm/exceptions.h"
 #include "vm/native_entry.h"
 #include "vm/object.h"
 #include "vm/symbols.h"
 
 namespace dart {
 
 DEFINE_FLAG(bool, trace_intrinsified_natives, false,
     "Report if any of the intrinsified natives are called");
 
 // Smi natives.
 
 // Returns false if integer is in wrong representation, e.g., as is a Bigint
 // when it could have been a Smi.
 static bool CheckInteger(const Integer& i) {
   if (i.IsBigint()) {
     const Bigint& bigint = Bigint::Cast(i);
     return !BigintOperations::FitsIntoSmi(bigint) &&
-        !BigintOperations::FitsIntoMint(bigint);
+        !BigintOperations::FitsIntoInt64(bigint);
   }
   if (i.IsMint()) {
     const Mint& mint = Mint::Cast(i);
     return !Smi::IsValid64(mint.value());
   }
   return true;
 }
 
 
 DEFINE_NATIVE_ENTRY(Integer_bitAndFromInteger, 2) {
@@ skipping 282 matching lines @@
 
 DEFINE_NATIVE_ENTRY(Bigint_bitNegate, 1) {
   const Bigint& value = Bigint::CheckedHandle(arguments->NativeArgAt(0));
   const Bigint& result = Bigint::Handle(BigintOperations::BitNot(value));
   ASSERT(CheckInteger(value));
   ASSERT(CheckInteger(result));
   return result.AsValidInteger();
 }
 
 }  // namespace dart