[Picture-in-Picture] Move LayoutTests to external/wpt

Bug: 806249
Change-Id: I46ccd72da19253fdb0ff54d90fd439a8d98ca5a9
Reviewed-on: https://chromium-review.googlesource.com/895447
Commit-Queue: Mounir Lamouri (slow) <mlamouri@chromium.org>
Reviewed-by: Mounir Lamouri (slow) <mlamouri@chromium.org>
Reviewed-by: apacible <apacible@chromium.org>
Cr-Commit-Position: refs/heads/master@{#534069}
8 files changed