[ios] Fix Default Browser Banner in the FRE

This change sets the bannerSize property in the Default Browser view
just as the signin screen already does. Below are screenshots showing
the appearance after this change.

Signin Screen:
https://screenshot.googleplex.com/7myVjkzZNvpKd7d.png

Default Browser Screen:
https://screenshot.googleplex.com/4RPbCEaFcrSeimF.png

Fixed: 345507382
Change-Id: If637ef181bf5f92840672294e76cabd2ad25e7d9
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5607827


Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Gauthier Ambard <gambard@chromium.org>
Commit-Queue: Scott Yoder <scottyoder@google.com>
Cr-Commit-Position: refs/heads/main@{#1312731}