This property represents the CSS content size, so let's reduce ambiguity
by using the spec terminology.
We also bring a bunch of related functions along for the ride.
This is poorly factored. TextNode needs to know whether the most
recently inserted fragment on the current line was empty or ended in
whitespace. This is used when deciding what to do with leading
whitespace in text nodes.
Let's keep this working for now, but we should eventually sort this out
and make text chunk iteration not depend on this information.
When collapsing whitespace, we can skip over all-whitespace chunks at
the start of each line, and immediately following fragments that
themselves end in whitespace.
We don't want to descend into inline-block containers when iterating
inline-level items, since that would make the inline-level children of
the inline-block bubble up to the containing block of the inline-block.
This patch adds a new mechanism that allows InlineFormattingContext to
build line boxes incrementally instead of all-in-one go.
Incremental build will eventually allow much better support for CSS
floating objects.
