Use webview provider for shell layout and ui webview tests.

This prepares the way to switch webview test bots to use swarmed devices.

Bug: 814405
Change-Id: Ic6c1f2b713392b3ed80b26dae1a5571de648914d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1526809
Reviewed-by: Ben Pastene <bpastene@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Commit-Queue: Andrew Luo <aluo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642127}
2 files changed