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

lib/protobuf_field.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.
 
 part of protoc;
 
 class ProtobufField {
   static final RegExp HEX_LITERAL_REGEX =
       new RegExp(r'^0x[0-9a-f]+$', multiLine: false, caseSensitive: false);
   static final RegExp INTEGER_LITERAL_REGEX = new RegExp(r'^[+-]?[0-9]+$');
@@ skipping 176 matching lines @@
           if (field.hasDefaultValue() && '0' != field.defaultValue) {
             initialization = '()${SP}=>${SP}${field.defaultValue}';
           }
         }
         break;
       case FieldDescriptorProto_Type.TYPE_INT64:
       case FieldDescriptorProto_Type.TYPE_UINT64:
       case FieldDescriptorProto_Type.TYPE_SINT64:
       case FieldDescriptorProto_Type.TYPE_FIXED64:
       case FieldDescriptorProto_Type.TYPE_SFIXED64:
-        baseType = 'ByteData';
-        typeString = write('ByteData');
+        baseType = 'Int64';
+        typeString = write('Int64');
         packable = true;
         switch (field.type) {
           case FieldDescriptorProto_Type.TYPE_INT64:
             codedStreamType = 'Int64';
             break;
           case FieldDescriptorProto_Type.TYPE_UINT64:
             codedStreamType = 'Uint64';
             break;
           case FieldDescriptorProto_Type.TYPE_SINT64:
             codedStreamType = 'Sint64';
@@ skipping 139 matching lines @@
         return 2; // Length-delimited
       case FieldDescriptorProto_Type.TYPE_GROUP:
         return 3; // Start group
       case FieldDescriptorProto_Type.TYPE_FLOAT:
       case FieldDescriptorProto_Type.TYPE_FIXED32:
       case FieldDescriptorProto_Type.TYPE_SFIXED32:
         return 5; // 32-bit
     }
   }
 }