Add myself as an owner of event_sender

Since I'm usually the one approving the blink side of input changes which
need changes in event_sender for their tests.

Review URL: https://codereview.chromium.org/774393004

Cr-Commit-Position: refs/heads/master@{#307143}

content/shell/renderer/test_runner/OWNERS

@@ -4,3 +4,5 @@ dpranke@chromium.org
 pfeldman@chromium.org
 tkent@chromium.org
 tommyw@chromium.org
+
+per-file event_sender.*=rbyers@chromium.org