Inline nodes in our layout tree have a position, so let's show it. By
centralizing the logic for this, block nodes now lose their redundant
'content-size' dump info which is already part of the box model dump.
Because we defined `th { text-align: center }` in our UA stylesheet, it
received a higher precedence than inherited (inline) styles. Firefox
deals with this by defining a custom `text-align` value that prioritizes
any inherited value before defaulting to `text-align: center`.
We now do this as well :^)
