Add support for a global configuration file.

lib/src/runner/configuration.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.
 
 import 'dart:io';
 
 import 'package:boolean_selector/boolean_selector.dart';
 import 'package:collection/collection.dart';
 import 'package:glob/glob.dart';
 import 'package:path/path.dart' as p;
@@ skipping 209 matching lines @@
     yield* presets.values;
   }
 
   /// Parses the configuration from [args].
   ///
   /// Throws a [FormatException] if [args] are invalid.
   factory Configuration.parse(List<String> arguments) => args.parse(arguments);
 
   /// Loads the configuration from [path].
   ///
+  /// If [global] is `true`, this restricts the configuration file to only rules
+  /// that are supported globally.
+  ///
   /// Throws an [IOException] if [path] does not exist or cannot be read. Throws
   /// a [FormatException] if its contents are invalid.
-  factory Configuration.load(String path) => load(path);
+  factory Configuration.load(String path, {bool global: false}) =>
+      load(path, global: global);
 
   factory Configuration({
       bool help,
       bool version,
       bool verboseTrace,
       bool jsTrace,
       bool skip,
       String skipReason,
       PlatformSelector testOn,
       bool pauseAfterLoad,
@@ skipping 259 matching lines @@
 
   /// Merges two maps whose values are [Configuration]s.
   ///
   /// Any overlapping keys in the maps have their configurations merged in the
   /// returned map.
   Map<Object, Configuration> _mergeConfigMaps(Map<Object, Configuration> map1,
           Map<Object, Configuration> map2) =>
       mergeMaps(map1, map2,
           value: (config1, config2) => config1.merge(config2));
 }