Fix touch hit rect position for table cells

RenderTableCell is unusual in that its location offset includes the offset of
its parent row.  We compensate for this in other places (like offsetFromContainer),
and so this CL also compensates for this in touch hit rect generation.

BUG=300283

Review URL: https://codereview.chromium.org/26964002

git-svn-id: svn://svn.chromium.org/blink/trunk@159498 bbb929c8-8fbe-4397-9dbb-9b2b20218538