Redo our benchmarks; add a benchmark/benchmarks.dart tool.

pkg/analysis_server/test/completion_test.dart

-// Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2017, 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.
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:test/test.dart';
 
 import 'completion_test_support.dart';
 
@@ skipping 2496 matching lines @@
       } else {
         ++expectedPassCount;
         test(testName, () {
           CompletionTestCase test = new CompletionTestCase();
           return test.runTest(spec, extraFiles);
         });
       }
     }
   }
 }