Clean up out/<target> directory in the end if extract_build.

build/android/buildbot/bb_device_steps.py

Index: build/android/buildbot/bb_device_steps.py
diff --git a/build/android/buildbot/bb_device_steps.py b/build/android/buildbot/bb_device_steps.py
index ca05438781244253c27267d8a55ccc1e1b4fe255..eac5342867c2078e1c65a78e9e70d81e5353fb3a 100755
--- a/build/android/buildbot/bb_device_steps.py
+++ b/build/android/buildbot/bb_device_steps.py
@@ -659,6 +659,9 @@ def MainTestWrapper(options):
     # KillHostHeartbeat() has logic to check if heartbeat process is running,
     # and kills only if it finds the process is running on the host.
     provision_devices.KillHostHeartbeat()
+    if options.cleanup:
+      shutil.rmtree(os.path.join(CHROME_OUT_DIR, options.target),
+          ignore_errors=True)
 
 
 def GetDeviceStepsOptParser():
@@ -704,6 +707,8 @@ def GetDeviceStepsOptParser():
       help='Do not run stack tool.')
   parser.add_option('--asan-symbolize',  action='store_true',
       help='Run stack tool for ASAN')
+  parser.add_option('--cleanup', action='store_true',
+      help='Delete out/<target> directory at the end of the run.')
   return parser