ui: Change ListModel::RemoveAt() API to return a scoped_ptr<ItemType>

This should make the ownership model more explicit, since it is very easy to
miss the ownership transfer.

Inspired by Xiyuan's comment in:

https://codereview.chromium.org/63123003/diff/80001/ui/app_list/app_list_item_list.h#newcode60

BUG=316924
TEST=app_list_unittests, ui_unittests
R=xiyuan@chromium.org
TBR=ben

Review URL: https://codereview.chromium.org/66823004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234108 0039d316-1c4b-4281-b951-d872f2087c98
Request 24-bit framebuffers when using xvfb-run.

xvfb-run defaults to 8-bit framebuffers, which was causing problems for Aura.

BUG=316687

Review URL: https://codereview.chromium.org/67423003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@234109 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 234108
SVN changes up to revision 234109