[iOS] Use ChromeEG class instead of App interface

This would allow the tree to build without reverting
crrev.com/c/5310020.

Change-Id: I036f52aeb4da9ac46cad9cd6e14303efbadb9598
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5314763


Owners-Override: Rainhard Findling <rainhard@chromium.org>
Commit-Queue: Arthur Milchior <arthurmilchior@chromium.org>
Commit-Queue: Filipa Senra <fsenra@google.com>
Commit-Queue: Rainhard Findling <rainhard@chromium.org>
Reviewed-by: Filipa Senra <fsenra@google.com>
Auto-Submit: Arthur Milchior <arthurmilchior@chromium.org>
Reviewed-by: Rainhard Findling <rainhard@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1263889}