cleanup: move fieldType constants and functions to a separate file

lib/src/protobuf/unknown_field_set.dart

 // Copyright (c) 2011, 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.
 
 part of protobuf;
 
 class UnknownFieldSet {
 
   final Map<int, UnknownFieldSetField> _fields =
       new Map<int, UnknownFieldSetField>();
@@ skipping 205 matching lines @@
       ..addAll(varints)
       ..addAll(fixed32s)
       ..addAll(fixed64s)
       ..addAll(groups);
 
   void writeTo(int fieldNumber, CodedBufferWriter output) {
     write(type, value) {
       output.writeField(fieldNumber, type, value);
     }
 
-    write(GeneratedMessage._REPEATED_UINT64, varints);
-    write(GeneratedMessage._REPEATED_FIXED32, fixed32s);
-    write(GeneratedMessage._REPEATED_FIXED64, fixed64s);
-    write(GeneratedMessage._REPEATED_BYTES, lengthDelimited);
-    write(GeneratedMessage._REPEATED_GROUP, groups);
+    write(FieldType._REPEATED_UINT64, varints);
+    write(FieldType._REPEATED_FIXED32, fixed32s);
+    write(FieldType._REPEATED_FIXED64, fixed64s);
+    write(FieldType._REPEATED_BYTES, lengthDelimited);
+    write(FieldType._REPEATED_GROUP, groups);
   }
 
   void addGroup(UnknownFieldSet value) {
     groups.add(value);
   }
 
   void addLengthDelimited(List<int> value) {
     lengthDelimited.add(value);
   }
 
   void addFixed32(int value) {
     fixed32s.add(value);
   }
 
   void addFixed64(Int64 value) {
     fixed64s.add(value);
   }
 
   void addVarint(Int64 value) {
     varints.add(value);
   }
 
   bool hasRequiredFields() => false;
 
   bool isInitialized() => true;
 
   int get length => values.length;
 }