[autotest] Fix missing import

BUG=chromium:715435
TEST=None

Change-Id: I48f2046bc65531d6de98ea52012a447ad14cbb3a
Reviewed-on: https://chromium-review.googlesource.com/497492
Commit-Ready: Allen Li <ayatane@chromium.org>
Tested-by: Allen Li <ayatane@chromium.org>
Reviewed-by: Aviv Keshet <akeshet@chromium.org>
diff --git a/site_utils/gs_offloader.py b/site_utils/gs_offloader.py
index 4efe992..581d43e 100755
--- a/site_utils/gs_offloader.py
+++ b/site_utils/gs_offloader.py
@@ -50,6 +50,7 @@
     from chromite.lib import metrics
     from chromite.lib import ts_mon_config
 except ImportError:
+    from autotest_lib import site_utils
     metrics = site_utils.metrics_mock
     ts_mon_config = site_utils.metrics_mock