GitLab

 - Add top-level JS/HTML files that will host the V3 version.
 - Use a JS import for the generated chromeos/search_handler.m.js
   as a proof of concept.
 - Update BUILD.gn files as needed.
 - Currently only works when optimize_webui = false

Bug: 1045266
Change-Id: I421f9090833731748d18ac2d19013faef3199648
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2171981Reviewed-by: dpapad <dpapad@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Nnamdi Theodore Johnson-kanu <tjohnsonkanu@google.com>
Cr-Commit-Position: refs/heads/master@{#766520}