Revert "Use native async/await support in pub."

tools/run_pub.py

 #!/usr/bin/env python
 # 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.
 """Used to run pub before the SDK has been built"""
 
 import argparse
 import os
 import platform
 import subprocess
 import sys
 
 SCRIPT_DIR = os.path.dirname(sys.argv[0])
 DART_ROOT = os.path.realpath(os.path.join(SCRIPT_DIR, '..'))
-PUB_PATH = os.path.join(DART_ROOT, 'sdk/lib/_internal/pub/bin/pub.dart')
+PUB_PATH = os.path.join(DART_ROOT,
+                        'sdk/lib/_internal/pub_generated/bin/pub.dart')
 CANARY_PATH = os.path.join(DART_ROOT, 'tools', 'canary.dart')
 
 usage = """run_pub.py --package-root=<package root>"""
 
 def BuildArguments():
   result = argparse.ArgumentParser(usage=usage)
   result.add_argument("--package-root", help="package root", default=None)
   result.add_argument("--dart-executable", help="dart binary", default=None)
   return result
 
@@ skipping 68 matching lines @@
   (options, args) = parser.parse_known_args()
   if not ProcessOptions(options, args):
     parser.print_help()
     return 1
   dart_executable = FindDartExecutable(options.dart_executable,
                                        options.package_root)
   return RunPub(dart_executable, options.package_root, args)
 
 
 if __name__ == '__main__':
-  sys.exit(main())
+  sys.exit(main());