Copy perf.dart into front_end/tool.

pkg/front_end/tool/perf.dart

 // Copyright (c) 2016, 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.
 
-/// An entrypoint used to run portions of analyzer and measure its performance.
-library analyzer_cli.tool.perf;
+/// An entrypoint used to run portions of front_end and measure its performance.
+library front_end.tool.perf;
 
 import 'dart:async';
 import 'dart:io' show exit;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/error/listener.dart';
 import 'package:analyzer/file_system/file_system.dart' show ResourceUriResolver;
 import 'package:analyzer/file_system/physical_file_system.dart'
     show PhysicalResourceProvider;
@@ skipping 177 matching lines @@
 }
 
 /// Report that metric [name] took [time] micro-seconds to process
 /// [scanTotalChars] characters.
 void report(String name, int time) {
   var sb = new StringBuffer();
   sb.write('$name: $time us, ${time ~/ 1000} ms');
   sb.write(', ${scanTotalChars * 1000 ~/ time} chars/ms');
   print('$sb');
 }