Mention the usecase of Traceable/Untraceable.
Use Traceable for primitive types and DOMString
Use Traceable for NodeFlags
Add overflow to child layer size

When creating child layers it is important to consider overflow when
determining the size of the layer. This also means that overflow should
not be too large, so also shrink block width down to the size of their
contained fragment. This means that a block that has been explicitly
sized to width:100px should be 100 pixels wide instead of the width of
its containing block.
Update to latest wpt
Added path space support (Fixes #2150)
Render in parallel
Allow render threads to be specified with -t
Add a command line option (-n) to use native threading, for testing.

I added this to test the impact of green threading.
Fix typos
Request termination for XHR
Merge pull request #2656 from Manishearth/xhr-terminate

Request termination for XHR
Handle JSAPI OOM failures by task failure as soon as possible.

We already ensure to fail the task if GetProtoObject returns null, as we don't
have a useful way to handle OOM, and we don't wish to thread the failure
through to some place where we could handle it in a useful way.

Unfortunately, we cannot ensure through the type system that none of those
functions returns null, so we use assertions to check it dynamically.
Merge pull request #2668 from Ms2ger/CreateInterfaceObjects-failures

Handle JSAPI OOM failures by task failure as soon as possible.
Stop pretending that CreateInterfaceObjects2 can return the interface object.

We do not currently support the case of a non-callback interface that doesn't
have an interface prototype object. (This case is not allowed by the WebIDL
specification; it was added to Gecko to allow feature-detecting the URL
interface. See <https://bugzilla.mozilla.org/show_bug.cgi?id=1026720>.)

It follows that, if we call CreateInterfaceObjects2 at all, we will call it
with a protoClass argument, so there is no reason to use a nullable pointer
type for that argument.

Moreover, if we had actually supported that case, the returned interface
object would have been stored in the interface prototype object cache, to ill
effect.
Merge pull request #2678 from Ms2ger/CreateInterfaceObjects2-protoClass

Stop pretending that CreateInterfaceObjects2 can return the interface object.
Use internal mutability for XMLHttpRequest.
Merge pull request #2663 from saneyuki/trace_comment

Mention the usecase of Traceable/Untraceable.
Merge pull request #2670 from fdipilla/ticket#2150

Added path space support (Fixes #2150)
Merge pull request #2669 from Manishearth/wpt_up

Update to latest wpt