Start using more typed units in the compositor

Now that rust-layers is starting to support typed units, we can use
them more thoroughly in the compositor. This is a step toward removing
as many untyped units as possible.
Fix task failure when loading wikipedia.

There is still an issue with alpha display, so there is
likely a problem elsewhere, but this at least allows the
page to load for now (ref #2554).
Merge pull request #3173 from mrobinson/typed-units-1

Start using more typed units in the compositor
Add support for borders on inline elements.

Fix ahem reftests on mac, by disabling text AA in reftest mode.

Also fix precision issues in font metrics to correct height
and baseline calculations.
Merge pull request #3195 from glennw/image-format

Fix task failure when loading wikipedia.
Make some of Node's members private.
Merge pull request #3182 from glennw/inline-text-border

Add support for borders on inline elements
Merge pull request #3202 from Ms2ger/node-priv-members

Make some of Node's members private; r=Manishearth
Implement the rules for parsing integers as defined by HTML, and use them for canvas.
Handle failure to parse the value of the width and height attributes on canvas elements (fixes #3200).

The remaining failures are due to the tests's use of getComputedStyle.
Unify fontconfig source code so that one branch builds on both linux + android.
Add a layout debug module. This outputs a trace of the layout process to a JSON
file which can be viewed in an external tool. It provides a timelapse view of
how the flow tree and fragments changed during the layout process, which makes
it easier to debug layout bugs.
Merge pull request #3201 from glennw/fc-platform-fixup

Unify fontconfig source code so that one branch builds on both linux + android
Merge pull request #3205 from Ms2ger/parse-integers

Parse canvas's width and height attributes according to the specification; r=jdm
Implement document.lastModified (fixes #2972, #3127).
Merge pull request #3204 from Ms2ger/2972-3127-lastModified

Implement document.lastModified (fixes #2972, #3127); r=jdm+Manishearth
Throw TypeErrors instead of uncatcheable exceptions in CodegenRust.py (fixes #347, #3065).
Added a fast no-message RPC interface to the layout task.
Merge pull request #3207 from Ms2ger/347-3065-typeerror

Throw TypeErrors instead of uncatcheable exceptions in CodegenRust.py (fixes #347, #3065).
Change scope macro to be a no-op in release builds.