Reenable the second wpt chunk.
layout: Remove `layout/extra.rs`.

Also, rename a few methods in layout that arguably had confusing names.
Implement TreeWalker
Adds support for table layout trace and updates viewer for tables.
Fix dimensionality of Au

Previously, we implemented:

Au * Au -> Au
Au / Au -> Au
Au % Au -> Au

... which are inconsistent. It should be:

Au * Au -> SquaredAu
Au / Au -> i32
Au % Au -> i32

or:

Au * i32 -> Au
Au / i32 -> Au
Au % i32 -> Au

I picked the latter.

Also, the multiplicative identity does not make sense
when multiplication take two different types.
Remove min/max functions from util::geometry. Use std::cmp instead.
Merge pull request #3393 from jdm/wptchunk2

Reenable the second wpt chunk.
Merge pull request #3401 from pcwalton/refactor-layout

layout: Remove `layout/extra.rs`.
Merge pull request #3253 from ChrisParis/TreeWalker

Implement TreeWalker
Add font-size absolute size keywords. Fix #3417.

Relative size keywords are still missing:
https://github.com/servo/servo/issues/3423
added valid license to tid.rs
Handle generated content with `display: block` correctly during flow
construction.

The iteration was incorrect here. Although it accidentally worked
before, it will cause problems when we have incremental style
recalculation.

The `after_block_iteration` reftest will become interesting once we have
incremental style recalc.
Merge pull request #3399 from pcwalton/fix-generated-content-iteration

Handle generated content with `display: block` correctly during flow
Fix typo in equality check
First steps of &JSRef -> JSRef conversion

Replace &JSRef with JSRef in the bulk of the generated code. This will
remove a level of indirection throughout all DOM code.

This patch doesn't change methods implemented on JSRef<T> to take `self`
rather than `&self`, and it leaves a few other uses of &JSRef, but those
changes can be made incrementally.
Merge pull request #3424 from SimonSapin/font-size-absolute

Add font-size absolute size keywords. Fix #3417
Merge pull request #3427 from cgaebel/add-license-to-tid

added valid license to tid.rs
Merge pull request #3422 from zwarich/jsref

First steps of &JSRef -> JSRef conversion
Merge pull request #3420 from glennw/table-debug

Adds support for table layout trace and updates viewer for tables.
Reintroduce Untraceable<T>.deref_mut() to make mem::replace() possible to Untracebale<T> field.

Some compile errors caused by the compiler's misreading comes back again :(
We re-use `deref()`explicitly to hide these errors.