Add better error messages to the webkit_tests step in the android buildbot code.

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 cb09e9081543ceaa89f1ebeabda5c9e2e6c7b956..9cc709d60cbeffcc6ec383dcef4a2b09e2a7048b 100755
--- a/build/android/buildbot/bb_device_steps.py
+++ b/build/android/buildbot/bb_device_steps.py
@@ -263,8 +263,12 @@ def RunWebkitLayoutTests(options):
 
   exit_code = RunCmd(['webkit/tools/layout_tests/run_webkit_tests.py'] +
                      cmd_args)
-  if exit_code == 254:  # AKA -1, internal error.
+  if exit_code == 254: # test_run_results.UNEXPECTED_ERROR_EXIT_STATUS
     bb_annotations.PrintMsg('?? (crashed or hung)')
+  elif exit_code == 253: # test_run_results.NO_DEVICES_EXIT_STATUS
+    bb_annotations.PrintMsg('?? (no devices found)')
+  elif exit_code == 252: # test_run_results.NO_TESTS_EXIT_STATUS
+    bb_annotations.PrintMsg('?? (no tests found)')
   else:
     full_results_path = os.path.join('..', 'layout-test-results',
                                      'full_results.json')