move performance measurement to benchmark/integration

pkg/analysis_server/benchmark/integration/instrumentation_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.instrumentation;
 
 import 'dart:convert';
 
 import 'package:analyzer/src/generated/java_engine.dart';
 import 'package:analyzer/instrumentation/instrumentation.dart';
@@ skipping 130 matching lines @@
         sb.writeCharCode(code);
       }
       ++index;
     }
     if (sb.isNotEmpty) {
       fields.add(sb.toString());
     }
     return fields;
   }
 }