chore(sysmon): add cache downloader in the proc metric

BUG=b:250926214
test=Ran unit tests

Change-Id: I1002d2d4d006c203b0cccc861ef9ef337d2468c6
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/chromite/+/3947315
Reviewed-by: Allen Li <ayatane@chromium.org>
Commit-Queue: Congbin Guo <guocb@chromium.org>
Auto-Submit: Congbin Guo <guocb@chromium.org>
Tested-by: Congbin Guo <guocb@chromium.org>
diff --git a/scripts/sysmon/proc_metrics.py b/scripts/sysmon/proc_metrics.py
index b54f765..139b583 100644
--- a/scripts/sysmon/proc_metrics.py
+++ b/scripts/sysmon/proc_metrics.py
@@ -36,6 +36,10 @@
         self._metrics = [
             _ProcessMetric("autoserv", test_func=_is_parent_autoserv),
             _ProcessMetric(
+                "cache-downloader",
+                test_func=partial(_is_process_name, "downloader")
+            ),
+            _ProcessMetric(
                 "common-tls", test_func=partial(_is_process_name, "common-tls")
             ),
             _ProcessMetric("curl", test_func=partial(_is_process_name, "curl")),