[autotest] Log result dir size to metadata

This is to help troubleshoot the result size.

BUG=chromium:524814
TEST=None

Change-Id: Ic51ab7911f4c559b9ee3af8b20a1df0c4f5e8a27
Reviewed-on: https://chromium-review.googlesource.com/295890
Commit-Ready: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
Reviewed-by: Mungyung Ryu <mkryu@google.com>
diff --git a/site_utils/gs_offloader.py b/site_utils/gs_offloader.py
index ed889e4..16dc609 100755
--- a/site_utils/gs_offloader.py
+++ b/site_utils/gs_offloader.py
@@ -44,7 +44,8 @@
 GS_OFFLOADING_ENABLED = global_config.global_config.get_config_value(
     'CROS', 'gs_offloading_enabled', type=bool, default=True)
 
-STATS_KEY = 'gs_offloader.%s' % socket.gethostname()
+STATS_KEY = 'gs_offloader.%s' % socket.gethostname().replace('.', '_')
+METADATA_TYPE = 'result_dir_size'
 
 timer = autotest_stats.Timer(STATS_KEY)
 
@@ -260,7 +261,11 @@
         kibibytes_transferred = get_directory_size_kibibytes(dir_entry)
 
         counter.increment('kibibytes_transferred_total', kibibytes_transferred)
-        autotest_stats.Gauge(STATS_KEY).send(
+        metadata = {'_type': METADATA_TYPE,
+                    'size_KB': kibibytes_transferred,
+                    'result_dir': dir_entry,
+                    'drone': socket.gethostname().replace('.', '_')}
+        autotest_stats.Gauge(STATS_KEY, metadata=metadata).send(
                 'kibibytes_transferred', kibibytes_transferred)
         counter.increment('jobs_offloaded')
         shutil.rmtree(dir_entry)