Auto merge of #23516 - pcwalton:webrenderup, r=pcwalton,jdm

Upgrade WebRender

This is against an old Servo because I can't build current Servo due to compile errors in RNG crates. I verified that it starts up.

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #23516
- [x] There are tests for these changes

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/23516)
<!-- Reviewable:end -->

components/canvas/webgl_thread.rs

@@ -659,7 +659,7 @@ impl<VR: WebVRRenderHandler + 'static> WebGLThread<VR> {
     /// Helper function to create a `webrender_api::ImageDescriptor`.
     fn image_descriptor(size: Size2D<i32>, alpha: bool) -> webrender_api::ImageDescriptor {
         webrender_api::ImageDescriptor {
-            size: webrender_api::DeviceIntSize::new(size.width, size.height),
+            size: webrender_api::units::DeviceIntSize::new(size.width, size.height),
             stride: None,
             format: webrender_api::ImageFormat::BGRA8,
             offset: 0,