Revert "Make Zone API strong mode clean."

utils/compiler/create_snapshot_entry.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:io';
-import 'dart:async';
 
 Future<String> getVersion(var rootPath) {
   var suffix = Platform.operatingSystem == 'windows' ? '.exe' : '';
   var printVersionScript = rootPath.resolve("tools/print_version.py");
   return Process
       .run("python$suffix", [printVersionScript.toFilePath()]).then((result) {
     if (result.exitCode != 0) {
       throw "Could not generate version";
     }
     return result.stdout.trim();
@@ skipping 68 matching lines @@
   getSnapshotGenerationFile(args, rootPath).then((result) {
     var wrapper = "${args['output_dir']}/utils_wrapper.dart";
     writeSnapshotFile(wrapper, result);
   });
 
   getDart2jsSnapshotGenerationFile(args, rootPath).then((result) {
     var wrapper = "${args['output_dir']}/dart2js.dart";
     writeSnapshotFile(wrapper, result);
   });
 }