Add isCompactWidth helper to ChromeEarlGrey.

The ui_util's isCompactWidth(which the CEG test-side helper
is supposed to invoke on the app-side).

This is part of EG1 to EG2 migration, which involves moving
EarlGrey code from app-side helpers into test code.
EarlGrey2 has multiprocess architecture,
where Chrome Test and Chrome App are separate processes.

Bug: 922813
Change-Id: I03eef2a1c83bef9f5053bb4f47f5541d58981354
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1740746
Commit-Queue: Maksym Onufriienko <monufriienko@chromium.org>
Reviewed-by: Eugene But <eugenebut@chromium.org>
Cr-Commit-Position: refs/heads/master@{#684876}
10 files changed