pkg/compiler: fix imports

pkg/compiler/lib/src/old_to_new_api.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.
 
 /// Implementation of the new compiler API in '../compiler_new.dart' through the
 /// old compiler API in '../compiler.dart'.
 
 library compiler.api.legacy;
 
 import 'dart:async' show EventSink, Future;
-import 'null_compiler_output.dart' show NullSink;
+
 import '../compiler.dart';
 import '../compiler_new.dart';
+import 'null_compiler_output.dart' show NullSink;
 
 /// Implementation of [CompilerInput] using a [CompilerInputProvider].
 class LegacyCompilerInput implements CompilerInput {
   final CompilerInputProvider _inputProvider;
 
   LegacyCompilerInput(this._inputProvider);
 
   @override
   Future readFromUri(Uri uri) {
     return _inputProvider(uri);
@@ skipping 19 matching lines @@
   final CompilerOutputProvider _outputProvider;
 
   LegacyCompilerOutput([this._outputProvider]);
 
   @override
   EventSink<String> createEventSink(String name, String extension) {
     if (_outputProvider != null) return _outputProvider(name, extension);
     return NullSink.outputProvider(name, extension);
   }
 }