WebUI: Add johntlee to owners

Change-Id: I43e9f2df360a20f4e1a8641114f897053f47bd60
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2358600Reviewed-by: dpapad <dpapad@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Commit-Queue: John Lee <johntlee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#798838}

ui/webui/PLATFORM_OWNERS

@@ -4,6 +4,7 @@ antrim@chromium.org  # CET
 calamity@chromium.org
 dpapad@chromium.org
 dschuyler@chromium.org
+johntlee@chromium.org
 khorimoto@chromium.org  # For Chrome OS changes.
 michaelpg@chromium.org  # For Chrome OS changes.
 rbpotter@chromium.org