Extract ClosedWorldImpl from WorldImpl.

pkg/compiler/lib/src/apiimpl.dart

 // Copyright (c) 2012, 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 leg_apiimpl;
 
 import 'dart:async';
 
 import 'package:package_config/packages.dart';
 import 'package:package_config/packages_file.dart' as pkgs;
@@ skipping 29 matching lines @@
   ForwardingResolvedUriTranslator resolvedUriTranslator;
 
   GenericTask userHandlerTask;
   GenericTask userProviderTask;
   GenericTask userPackagesDiscoveryTask;
 
   Uri get libraryRoot => options.platformConfigUri.resolve(".");
 
   CompilerImpl(this.provider, api.CompilerOutput outputProvider, this.handler,
       CompilerOptions options,
-      {MakeBackendFuncion makeBackend, MakeReporterFunction makeReporter})
+      {MakeBackendFunction makeBackend, MakeReporterFunction makeReporter})
       // NOTE: allocating measurer is done upfront to ensure the wallclock is
       // started before other computations.
       : measurer = new Measurer(enableTaskMeasurements: options.verbose),
         resolvedUriTranslator = new ForwardingResolvedUriTranslator(),
         super(
             options: options,
             outputProvider: outputProvider,
             environment: new _Environment(options.environment),
             makeBackend: makeBackend,
             makeReporter: makeReporter) {
@@ skipping 334 matching lines @@
   }
 }
 
 /// For every 'dart:' library, a corresponding environment variable is set
 /// to "true". The environment variable's name is the concatenation of
 /// this prefix and the name (without the 'dart:'.
 ///
 /// For example 'dart:html' has the environment variable 'dart.library.html' set
 /// to "true".
 const String _dartLibraryEnvironmentPrefix = 'dart.library.';