Update the protocol buffer compiler plugin to use Int64 from the fixnum package

test/validate_fail_test.dart

 #!/usr/bin/env dart
 // 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.
 
 library validate_fail_test;
 
 import 'dart:typed_data';
 
 import 'package:protobuf/protobuf.dart';
@@ skipping 11 matching lines @@
   test('testValidatePbListTypes', () {
 
     PbList<int> lSint32 = new PbSint32List();
     expect(() { lSint32.add(-2147483649); }, throwsArgumentError);
     expect(() { lSint32.add(2147483648); }, throwsArgumentError);
 
     PbList<int> lUint32 = new PbUint32List();
     expect(() { lUint32.add(-1); }, throwsArgumentError);
     expect(() { lUint32.add(4294967296); }, throwsArgumentError);
 
-    PbList<ByteData> lSint64 = new PbSint64List();
+    PbList<Int64> lSint64 = new PbSint64List();
     expect(() { lSint64.add(-9223372036854775809); }, badArgument);
     expect(() { lSint64.add(9223372036854775808); }, badArgument);
 
-    PbList<ByteData> lUint64 = new PbUint64List();
+    PbList<Int64> lUint64 = new PbUint64List();
     expect(() { lUint64.add(-1); }, badArgument);
     expect(() { lUint64.add(18446744073709551616); }, badArgument);
 
     PbList<double> lFloat = new PbFloatList();
     expect(() { lFloat.add(-3.4028234663852886E39); }, throwsArgumentError);
     expect(() { lFloat.add(3.4028234663852886E39); }, throwsArgumentError);
   });
 
   test('testValidationFailureMessages', () {
     TestAllTypes builder = new TestAllTypes();
@@ skipping 74 matching lines @@
 
     // Unknown type.
     expect(() { builder.setField(1, 1, 24); }, throwsArgumentError);
 
     expect(() {
       new TestAllExtensions()
           .setExtension(Unittest.optionalInt32Extension, '101');
     }, throwsArgumentError);
   });
 }