[Extensions OOPI] Update app window bindings for OOPI

      Update the app window custom bindings to use render frame logic
instead of render view logic.  This involves changes to the custom
bindings themselves, as well as app window creation logic. And, for fun,
a few small cleanups while I was in the area.

BUG=455776
TBR=dbeam@chromium.org (webui)

Review URL: https://codereview.chromium.org/1211003006

Cr-Commit-Position: refs/heads/master@{#338076}