Revert 229030 "list.js: Prevent the list from focusing to the bo..."

> list.js: Prevent the list from focusing to the bottom of the list
> 
> When the lead item was taken off the selected items, the last selected item became the new lead item. But this behaviour made the list scrolled to the last. With this patch, in such case, the nearest item becomes the new lead item instead. This fixes the issue of crbug.com/276827.
> 
> BUG=276827
> TEST=manually tested
> R=nkostylev@chromium.org
> 
> Review URL: https://codereview.chromium.org/26705006

TBR=yoshiki@chromium.org

Review URL: https://codereview.chromium.org/27590005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@229057 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 229057