DOMUI: Fix list selection when zoomed in or out
DOMUI: Fix list selection when zoomed in or out

This is probably the third fix to this code. WebKit is really buggy when it
comes to reporting sizes and positions in different zoom settings.

This time there are 2 changes. Instead of using offsetHeight I switched to use
getBoundingClientRect().height which is a double (not floored). Secondly, to
find the item at a certain y position I now use the middle point of the item
(previously we used the top of the item).

BUG=72208
TEST=Go to bookmarks manager
     Zoom in or out by pressing Ctrl/Command + or -
     Go to a folder with more a lots of items (30?)
     All items should be clickable in all zoom settings

Review URL: http://codereview.chromium.org/6448006

git-svn-id: http://src.chromium.org/svn/trunk/src@74166 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: c2ef0162c01757c83c5b814685dcfb91b3f576ff
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser