This CL sets a preferred size of (540, 820) for the preferred size
on iPad for the Default Search Engine Choice view.

It follows the documentation here:
https://developer.apple.com/documentation/uikit/uimodalpresentationstyle/uimodalpresentationformsheet?language=objc

Screenshots (Google-internal):
https://docs.google.com/document/d/1QI4kOf1GRCE9koCjNQS9MYzN9Q1ATtroHFovA8Wn0YY/edit?usp=sharing

Fixed: 331195422

(cherry picked from commit 7f37e895de8f9b97296050291792c980df84210f)

Change-Id: I614a75f4e99a1d1333140d238f48880bb5d588b3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5388186
Commit-Queue: Mihai Sardarescu <msarda@chromium.org>
Reviewed-by: Jérôme Lebel <jlebel@chromium.org>
Cr-Original-Commit-Position: refs/heads/main@{#1277705}
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5393283
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Owners-Override: Krishna Govind <govind@chromium.org>
Reviewed-by: Krishna Govind <govind@chromium.org>
Cr-Commit-Position: refs/branch-heads/6379@{#4}
Cr-Branched-From: e5b4774389ecb8a127e4fc8afbc7c2e781b67716-refs/heads/main@{#1277564}