Remove "layouttest" or "layout test" in //content

They are renamed to "webtest" or "web test".
This CL has no behavior changes.

TBR=caitkp@chromium.org, mkwst@chromium.org

Bug: 843412
Change-Id: Ifdd22e1bfd10e727e17c2035b3faf1ae4fec1400
Reviewed-on: https://chromium-review.googlesource.com/c/1367391
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615044}
109 files changed