Use "package:" imports for pub.

lib/src/dart.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.
 
 /// A library for compiling Dart code and manipulating analyzer parse trees.
 library pub.dart;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
 import 'package:analyzer/analyzer.dart';
-import 'package:path/path.dart' as path;
-
 import 'package:compiler_unsupported/compiler.dart' as compiler;
 import 'package:compiler_unsupported/src/filenames.dart'
     show appendSlash;
+import 'package:path/path.dart' as path;
 
 import 'asset/dart/serialize.dart';
 import 'io.dart';
 import 'log.dart' as log;
 
 /// Interface to communicate with dart2js.
 ///
 /// This is basically an amalgamation of dart2js's
 /// [compiler.CompilerInputProvider], [compiler.CompilerOutputProvider], and
 /// [compiler.DiagnosticHandler] function types so that we can provide them
@@ skipping 188 matching lines @@
   Isolate.spawnUri(Uri.parse(message['uri']), [], message['message'],
           packageRoot: packageRoot)
       .then((_) => replyTo.send({'type': 'success'}))
       .catchError((e, stack) {
     replyTo.send({
       'type': 'error',
       'error': CrossIsolateException.serialize(e, stack)
     });
   });
 }