Replace ash::HighlighterControllerObserver with a mojo client

This makes metalayer/highlighter features fully mash-compatible.

Bug: 769994

Test: ash_unittests --gtest_filter=Palette*
Change-Id: I8344ffdd246357cc14866cf19dbfcc9644be00e5
Reviewed-on: https://chromium-review.googlesource.com/693346
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Luis Hector Chavez <lhchavez@chromium.org>
Reviewed-by: David Reveman <reveman@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Commit-Queue: Vladislav Kaznacheev <kaznacheev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508366}
23 files changed