Remove use of deprecated get_mut_ref
Merge pull request #3478 from zwarich/get-mut-ref

Remove use of deprecated get_mut_ref

Reviewed-by: metajack
layout: Unify the block-size computation for blocks and floats.

The float code was old and did not support most of CSS 2.1. So unifying
the two paths both simplifies code and improves functionality.

Improves the Reddit sidebar.
Merge pull request #3472 from pcwalton/unify-block-and-float-layout

layout: Unify the block-size computation for blocks and floats.

Reviewed-by: glennw
layout: Block formatting contexts should contain all their floats.

Improves Pinterest considerably.