pkg/compiler: fix imports

pkg/compiler/lib/compiler.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 compiler;
 
 import 'dart:async';
+
 import 'package:package_config/packages.dart';
+
 import 'compiler_new.dart' as new_api;
+import 'src/old_to_new_api.dart';
 import 'src/options.dart' show CompilerOptions;
-import 'src/old_to_new_api.dart';
 
 // Unless explicitly allowed, passing [:null:] for any argument to the
 // methods of library will result in an Error being thrown.
 
 /**
  * Returns a future that completes to the source corresponding to [uri].
  * If an exception occurs, the future completes with this exception.
  *
  * The source can be represented either as a [:List<int>:] of UTF-8 bytes or as
  * a [String].
@@ skipping 176 matching lines @@
   final String name;
 
   /**
    * This constructor is not private to support user-defined
    * diagnostic kinds.
    */
   const Diagnostic(this.ordinal, this.name);
 
   String toString() => name;
 }