Getting these down to the embedding API level required that I redo the bindings generator again, so this is more commits than anticipated.
@mbrubeck @Manishearth @pcwalton but NOT @larsbergstrom so don't even look at this.
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/6219)
<!-- Reviewable:end -->
This fixes various race conditions that affect test execution when using the servodriver product. It doesn't yet do enough to make servodriver a viable alternative to the normal servo test executor.
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/6161)
<!-- Reviewable:end -->
* Wait for the correct pipeline to return a LoadComplete message
before signalling a load is complete, and ensure that the root
pipeline is the one corresponding to the active document of the top
level browsing context, even if this has not yet painted.
* Ensure that TakeScreenshot operates on the correct pipeline
* Reset the screenshot ready flag whenever we decide that we are ready
to take a screenshot.
The basic idea is it's safe to output an image for reftest by testing:
- That the compositor doesn't have any animations active.
- That the compositor is not waiting on any outstanding paint messages to arrive.
- That the script tasks are "idle" and therefore won't cause reflow.
- This currently means page loaded, onload fired, reftest-wait not active, first reflow triggered.
- It could easily be expanded to handle pending timers etc.
- That the "epoch" that the layout tasks have last laid out after script went idle, is reflected by the compositor in all visible layers for that pipeline.
Spec: http://dev.w3.org/csswg/css-device-adapt/
Currently, the actual viewport is used by the layout task as part of the reflow, and the compositor uses the zoom constraints. I'm not sure if anywhere else currently needs access to the constraints (i.e. there's no CSSOM as far as I can tell).
I did not implement sections 9 (viewport <META>) or 10 (handling 'auto' for 'zoom').
<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/5361)
<!-- Reviewable:end -->
This is incomplete in several ways:
* It assumes that there's only one constellation (i.e. top level browsing context), ever.
* The session support is very basic indeed (no capabilities)
* Passing channels over channels may not sit well with IPC
* The error handling is mostly missing
Transition events are not yet supported, and the only animatable
properties are `top`, `right`, `bottom`, and `left`. However, all other
features of transitions are supported. There are no automated tests at
present because I'm not sure how best to test it, but three manual tests
are included.
