IME: Delegate ui::InputMethod construction to ozone

This gives ui::OzonePlatform control over ui::InputMethod creation in
ozone builds.

Bug: 943789, 978970
Test: various builds, ui_unittests

Change-Id: Ie7f8977bf2d36df4ed84cfcae5254add27aa97eb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1531600
Commit-Queue: Michael Spang <spang@chromium.org>
Reviewed-by: Shu Chen <shuchen@chromium.org>
Reviewed-by: Antonio Gomes <tonikitoo@igalia.com>
Cr-Commit-Position: refs/heads/master@{#674959}
23 files changed