top and bottom black background line not getting displayed

The table cell's background was not being displayed. Since the table
cell had no child correct offsetWidth was not being set even if table
width is being defined.

cellHasContent should also be set to true incase background color is
present.

I already landed this patch on Webkit. Just modified the layout test file. 
http://trac.webkit.org/changeset/160410.

R=jchaffraix@chromium.org
BUG=343482

Review URL: https://codereview.chromium.org/163163002

git-svn-id: svn://svn.chromium.org/blink/trunk@168119 bbb929c8-8fbe-4397-9dbb-9b2b20218538