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

test/unknown_field_set_test.dart

Index: test/unknown_field_set_test.dart
diff --git a/test/unknown_field_set_test.dart b/test/unknown_field_set_test.dart
index 039ff78ab75c904400b9742e6db77cfd3ac4709d..8ff4d9df20f37497514932d17b496a50315fd3dc 100755
--- a/test/unknown_field_set_test.dart
+++ b/test/unknown_field_set_test.dart
@@ -69,10 +69,7 @@ void main() {
 
   test('testFixed64', () {
     UnknownFieldSetField optionalFixed64 = getField('optionalFixed64');
-    expect(optionalFixed64.fixed64s[0].getUint32(0),
-           testAllTypes.optionalFixed64.getUint32(0));
-    expect(optionalFixed64.fixed64s[0].getUint32(4),
-           testAllTypes.optionalFixed64.getUint32(4));
+    expect(optionalFixed64.fixed64s[0], testAllTypes.optionalFixed64);
   });
 
   test('testLengthDelimited', () {