We should probably look to reuse the existing AddToHomescreenManager/DataFetcher code that exists for Android. This does the proper PWA checking, which isn't yet done on desktop when using add to shelf. That code could be made cross-platform with platform-specific subclasses like the app banner code.

For now, just remove these two things when behind the new feature flag (name TBA). Eventually, we'll want the PWA check logic, and allow editing when it's a non-PWA, but for now just remove it so we can get a feel for the experience.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/e849b5187b2fc04e70742394466624c934ccf8cb

commit e849b5187b2fc04e70742394466624c934ccf8cb
Author: Christopher Lam <calamity@chromium.org>
Date: Tue Oct 31 06:03:53 2017

[desktop-pwas] Remove 'Open as window' checkbox from bookmark app dialog.

This CL removes the 'Open as window' checkbox from the bookmark app
dialog when DesktopPWAWindowing is enabled and chooses to open as a
window if the site is an installable PWA and as a tab otherwise.

This requires adding an InstallableManager to the BookmarkAppHelper to
determine if the site is an installable PWA.

Bug:  729922 
Change-Id: I30d6329d52a9fabe314e6a8b76aa46e209cd171f
Reviewed-on: https://chromium-review.googlesource.com/700137
Reviewed-by: Ben Wells <benwells@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Commit-Queue: calamity <calamity@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512761}
[modify] https://crrev.com/e849b5187b2fc04e70742394466624c934ccf8cb/chrome/browser/banners/app_banner_infobar_delegate_desktop.cc
[modify] https://crrev.com/e849b5187b2fc04e70742394466624c934ccf8cb/chrome/browser/extensions/bookmark_app_helper.cc
[modify] https://crrev.com/e849b5187b2fc04e70742394466624c934ccf8cb/chrome/browser/extensions/bookmark_app_helper.h
[modify] https://crrev.com/e849b5187b2fc04e70742394466624c934ccf8cb/chrome/browser/extensions/bookmark_app_helper_unittest.cc
[modify] https://crrev.com/e849b5187b2fc04e70742394466624c934ccf8cb/chrome/browser/extensions/favicon_downloader.cc
[modify] https://crrev.com/e849b5187b2fc04e70742394466624c934ccf8cb/chrome/browser/extensions/favicon_downloader.h
[modify] https://crrev.com/e849b5187b2fc04e70742394466624c934ccf8cb/chrome/browser/ui/views/extensions/bookmark_app_confirmation_view.cc

Looks done to me.