GitLab

- Added |IsLSSEnabled| to help_app_ui.mojom.
- LSS methods in receiver forward requests via message pipe.
- Implement message handlers in browser_proxy.
- Added browsertest to ensure LSS methods used by delegate.

Bug: b/166047521
Change-Id: Iadc5fba94e79631d7b293be0e5b917f72bdc8fc8
Cq-Include-Trybots: chrome/try:linux-chromeos-chrome
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2437560Reviewed-by: Trent Apted <tapted@chromium.org>
Reviewed-by: dstockwell <dstockwell@google.com>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: Callistus Tan <callistus@google.com>
Cr-Commit-Position: refs/heads/master@{#813011}