GitLab

This creates a new FileTransferMessageHandler on a separate data
channel, which can send the host's RTC event log as a file-download.

Bug: 1122798
Change-Id: Icb76e63a790054c45d540c5f20222edbd2086b4d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2450891
Commit-Queue: Lambros Lambrou <lambroslambrou@chromium.org>
Reviewed-by: Erik Jensen <rkjnsn@chromium.org>
Cr-Commit-Position: refs/heads/master@{#814511}