GitLab

WebviewService will eventually be deprecated, this allows
PlatformViewsService to create webviews.

Bug: Internal b/144275588
Test: Build cast_shell
Change-Id: I96251d199d7c466e13be5fc05769a1d0c4717beb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1907076Reviewed-by: Daniel Nicoara <dnicoara@chromium.org>
Commit-Queue: Shawn Gallea <sagallea@google.com>
Cr-Commit-Position: refs/heads/master@{#714298}