Merge DefaultShelfView into ShelfView

This cl merges the DefaultShelfView into ShelfView class.

Bug: 977019
Change-Id: Ia02e0b3a2a122785fdcc9dfc5a7456ccdf0e448b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1699202
Commit-Queue: Yilkal Abe <yilkal@chromium.org>
Reviewed-by: James Cook <jamescook@chromium.org>
Reviewed-by: Aga Wronska <agawronska@chromium.org>
Reviewed-by: Manu Cornet <manucornet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676989}