commit bc7df44746143ce68c5d0226732caeeb79000f8e
author Ben Kwa <kenobi@google.com> Tue Feb 02 23:00:02 2016 -0800
committer Ben Kwa <kenobi@google.com> Tue Feb 09 18:06:11 2016 +0000
tree 50749d97b821f64e5ccf23877f38e4994f06508c
parent 64a451aa3a01f1284e41b1572206bddf9270861a

Implement PgUp/PgDn support.  (cherry-pick DO NOT MERGE)

- Clean up our LayoutManager code.  We actually only need a single
  layout manager, since a GridLayoutManager is a LinearLayoutManager,
  and list layout is simply grid layout with one column.  Make it so.

- Use the layout manager to compute item offsets for one page's worth of
  items.  Use that to implement page up/page down.

BUG=25195770

Change-Id: I23ddd5fd38532682e7f099b44e188d8c3fec02be
(cherry picked from commit 4d4bf9a21a16bae3497f94dbb558a2ede9d989ee)