Change owners for tools/perf/page_sets/webrtc_cases.

Bug: None
Change-Id: Id707947db395ea3c25b418b52520630fa479d5bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2283310Reviewed-by: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Mirko Bonadei <mbonadei@chromium.org>
Cr-Commit-Position: refs/heads/master@{#785870}

tools/perf/page_sets/webrtc_cases/OWNERS

-ehmaldonado@chromium.org
-jansson@chromium.org
+mbonadei@chromium.org
+glahiru@google.com