WebApp: Move WebAppBrowserController into web_app

WebAppBrowserController is now defined in chrome/browser/ui/web_applications/
and renamed to AppBrowserController.

It is the abstract superclass for the controllers for two types of apps:
- HostedAppBrowserController for extension based apps
- ManifestWebAppBrowserController for web apps (e.g. PWAs)

Change-Id: Iec4cf2e73f53873ef274fdc51f25375361efb698
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1600920
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Alexey Baskakov <loyso@chromium.org>
Commit-Queue: Eric Willigers <ericwilligers@chromium.org>
Cr-Commit-Position: refs/heads/master@{#658691}
27 files changed