devtools: flush stdout after printing android observatory address.

R=tonyg@chromium.org

Review URL: https://codereview.chromium.org/1861223002 .

Cr-Mirrored-From: https://github.com/domokit/mojo
Cr-Mirrored-Commit: de36acac2de0bdc434b5a1bf7586fb1b8d016359

devtoolslib/android_shell.py

diff --git a/devtoolslib/android_shell.py b/devtoolslib/android_shell.py
index ca7d5c1..daa2443 100644
--- a/devtoolslib/android_shell.py
+++ b/devtoolslib/android_shell.py
@@ -395,6 +395,7 @@
           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)