Support add to apps dialog for touchless

Add touchless support for the "add to home screen" dialog. This patch
includes support for the "custom" view in the touchless dialog
(something supported by normal modal dialogs). The touchless dialog
extends the original "add to homescreen" dialog to keep most call
sites unchanged.

Bug: 963516
Change-Id: I8e0ce32a75127630702fc697330e52fea51b18f2
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1613373
Commit-Queue: Matthew Jones <mdjones@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#660455}
8 files changed