Add wfh@chromium.org to ipc OWNERS files

Followup to https://codereview.chromium.org/550503003 that missed
//content/public/common/OWNERS.

BUG=None

Review URL: https://codereview.chromium.org/588493003

Cr-Commit-Position: refs/heads/master@{#295939}

content/public/common/OWNERS

@@ -10,3 +10,4 @@ per-file *param_traits*.h=kenrb@chromium.org
 per-file *param_traits*.h=nasko@chromium.org
 per-file *param_traits*.h=palmer@chromium.org
 per-file *param_traits*.h=tsepez@chromium.org
+per-file *param_traits*.h=wfh@chromium.org