Make pub strong-mode clean.

lib/src/barback/dart2js_transformer.dart

 // Copyright (c) 2013, 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:convert';
 
 import 'package:analyzer/analyzer.dart';
 import 'package:barback/barback.dart';
+import 'package:collection/collection.dart';
 import 'package:path/path.dart' as p;
 import 'package:pool/pool.dart';
 
 import 'package:compiler_unsupported/compiler.dart' as compiler;
 import 'package:compiler_unsupported/src/dart2js.dart'
     show AbortLeg;
 import 'package:compiler_unsupported/src/io/source_file.dart';
 import '../barback.dart';
 import '../dart.dart' as dart;
 import '../utils.dart';
@@ skipping 127 matching lines @@
         terse: _configBool('terse'),
         includeSourceMapUrls: _generateSourceMaps);
   }
 
   /// Parses and returns the "commandLineOptions" configuration option.
   List<String> get _configCommandLineOptions {
     if (!_settings.configuration.containsKey('commandLineOptions')) return null;
 
     var options = _settings.configuration['commandLineOptions'];
     if (options is List && options.every((option) => option is String)) {
-      return options;
+      return DelegatingList.typed(options);
     }
 
     throw new FormatException('Invalid value for '
         '\$dart2js.commandLineOptions: ${JSON.encode(options)} (expected list '
         'of strings).');
   }
 
   /// Parses and returns the "environment" configuration option.
   Map<String, String> get _configEnvironment {
     if (!_settings.configuration.containsKey('environment')) {
       return _environment.environmentConstants;
     }
 
     var environment = _settings.configuration['environment'];
     if (environment is Map &&
         environment.keys.every((key) => key is String) &&
         environment.values.every((key) => key is String)) {
-      return mergeMaps(environment, _environment.environmentConstants);
+      return mergeMaps(
+          DelegatingMap.typed(environment),
+          _environment.environmentConstants);
     }
 
     throw new FormatException('Invalid value for \$dart2js.environment: '
         '${JSON.encode(environment)} (expected map from strings to strings).');
   }
 
   /// Parses and returns a boolean configuration option.
   ///
   /// [defaultsTo] is the default value of the option.
   bool _configBool(String name, {bool defaultsTo: false}) {
@@ skipping 223 matching lines @@
   }
 }
 
 /// An [EventSink] that discards all data. Provided to dart2js when we don't
 /// want an actual output.
 class NullSink<T> implements EventSink<T> {
   void add(T event) {}
   void addError(errorEvent, [StackTrace stackTrace]) {}
   void close() {}
 }