update_engine: Make utils::FormatTimeDelta() work with negative values.
BUG=chromium:401862
TEST=New unit test + unit tests pass.
Change-Id: I89b7ec72c11b792d4353eb6b36b23eac4f82107d
Reviewed-on: https://chromium-review.googlesource.com/212878
Reviewed-by: Mike Frysinger <vapier@chromium.org>
Reviewed-by: Alex Deymo <deymo@chromium.org>
Commit-Queue: David Zeuthen <zeuthen@chromium.org>
Tested-by: David Zeuthen <zeuthen@chromium.org>
diff --git a/utils.h b/utils.h
index 8c4850e..6d14fbc 100644
--- a/utils.h
+++ b/utils.h
@@ -326,7 +326,8 @@
// as necessary; for example, an output of 5d2h0m15.053s means that the input
// time was precise to the milliseconds only. Zero padding not applied, except
// for fractions. Seconds are always shown, but fractions thereof are only shown
-// when applicable.
+// when applicable. If |delta| is negative, the output will have a leading '-'
+// followed by the absolute duration.
std::string FormatTimeDelta(base::TimeDelta delta);
// This method transforms the given error code to be suitable for UMA and