[content-service] Enable in-process Mac usage

Changes in-process NavigableContentsView to work on any platform
supporting Views UI rather than restricting it to Aura platforms.

Adapts simple_browser to run in a non-Aura environment as well.

Bug: 855092
Test: Run DCHECK build of chrome --launch-in-process-simple-browser on Mac
Change-Id: Ibdf7ccd83a4c2f3d2c4d667898d3723166c257a3
Reviewed-on: https://chromium-review.googlesource.com/1178802
Commit-Queue: Ken Rockot <rockot@chromium.org>
Reviewed-by: Alex Moshchuk <alexmos@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584349}
15 files changed