devtools: flush stdout after printing android observatory address.

mojo/devtools/common/devtoolslib/android_shell.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 import atexit
 import hashlib
 import logging
 import os
 import os.path
 import random
@@ skipping 377 matching lines @@
         line = logcat.stdout.readline()
         if not line:
           break
         match = re.search(r'Observatory listening on http://127.0.0.1:(\d+)',
                           line)
         if match:
           device_port = int(match.group(1))
           host_port = self._forward_host_port_to_device(0, device_port)
           print ('Dart observatory available at the host at http://127.0.0.1:%d'
                  % host_port)
+          sys.stdout.flush()
 
     logcat_watch_thread = threading.Thread(
         target=_forward_observatories_as_needed)
     logcat_watch_thread.daemon = True
     logcat_watch_thread.start()
 
   def forward_flutter_observatory_port(self):
     """Forwards the fixed port on which Flutter observatory is run."""
     self._forward_host_port_to_device(_FLUTTER_OBSERVATORY_PORT,
                                       _FLUTTER_OBSERVATORY_PORT)
@@ skipping 41 matching lines @@
           Results.output = rf.read()
 
     run_thread = threading.Thread(target=do_run)
     run_thread.start()
     run_thread.join(timeout)
 
     if run_thread.is_alive():
       self.stop_shell()
       return None, Results.output, True
     return None, Results.output, False