move performance measurement to benchmark/integration

pkg/analysis_server/benchmark/integration/log_file_input_converter.dart

 // Copyright (c) 2015, 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 input.transformer.log_file;
 
 import 'dart:convert';
 
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:logging/logging.dart';
@@ skipping 65 matching lines @@
     while (index < line.length) {
       int code = line.codeUnitAt(index);
       if (code < ZERO || NINE < code) {
         return line.substring(0, index);
       }
       ++index;
     }
     return line;
   }
 }