sysmon: Fix default type TypeError

BUG=chromium:787904
TEST=None

Change-Id: Ibc2e48f04c130ba750f901d995deecdb34803348
Reviewed-on: https://chromium-review.googlesource.com/786430
Commit-Ready: Allen Li <ayatane@chromium.org>
Tested-by: Allen Li <ayatane@chromium.org>
Reviewed-by: Ningning Xia <nxia@chromium.org>
diff --git a/scripts/sysmon/puppet_metrics.py b/scripts/sysmon/puppet_metrics.py
index f55efb8..81b0ffd 100644
--- a/scripts/sysmon/puppet_metrics.py
+++ b/scripts/sysmon/puppet_metrics.py
@@ -89,7 +89,7 @@
     """Return mapping of time information."""
     times = self._data.get('time', {}).copy()
     times.pop('last_run', None)
-    total = times.pop('total', None)
+    total = times.pop('total', 0)
     times['other'] = max(0, total - sum(times.itervalues()))
     return times