Add option to output device status to a JSON file.

BUG=392938
R=navabi@chromium.org, tonyg@chromium.org

Review URL: https://codereview.chromium.org/383933003

git-svn-id: http://src.chromium.org/svn/trunk/src/build@282728 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/buildbot/bb_device_status_check.py

@@ -5,6 +5,7 @@
 # found in the LICENSE file.
 
 """A class to keep track of devices across builds and report state."""
+import json
 import logging
 import optparse
 import os
@@ -275,6 +276,8 @@ def main():
                     help='Output device status data for dashboard.')
   parser.add_option('--restart-usb', action='store_true',
                     help='Restart USB ports before running device check.')
+  parser.add_option('--json-output',
+                    help='Output JSON information into a specified file.')
 
   options, args = parser.parse_args()
   if args:
@@ -359,6 +362,16 @@ def main():
                                                 [battery], '%',
                                                 'unimportant')
 
+  if options.json_output:
+    with open(options.json_output, 'wb') as f:
+      f.write(json.dumps({
+        'online_devices': devices,
+        'offline_devices': offline_devices,
+        'expected_devices': expected_devices,
+        'unique_types': unique_types,
+        'unique_builds': unique_builds,
+      }))
+
   if False in fail_step_lst:
     # TODO(navabi): Build fails on device status check step if there exists any
     # devices with critically low battery. Remove those devices from testing,