[Rounded Windows] Nit: Renamed helper method related to RoundedWindow

feature.

Bug: 1434781
Change-Id: I6131726be10c7fcde21167e3ca01dba7d96a380d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4641278


Reviewed-by: Sean Kau <skau@chromium.org>
Commit-Queue: Zoraiz Naeem <zoraiznaeem@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1161970}