Auto merge of #27295 - asajeffrey:gstreamer-webxr, r=Manishearth

Gstreamer plugin support for streaming from webxr

<!-- Please describe your changes on the following line: -->

Allows us to stream webxr video content.

---
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes do not require tests because we don't reftest the gstreamer plugin

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Cargo.lock

@@ -5072,6 +5072,7 @@ dependencies = [
  "surfman",
  "surfman-chains",
  "surfman-chains-api",
+ "webxr",
 ]
 
 [[package]]
@@ -6779,7 +6780,7 @@ dependencies = [
 [[package]]
 name = "webxr"
 version = "0.0.1"
-source = "git+https://github.com/servo/webxr#d9ec2263b017d9c415ce35e0f4417a454564bcf2"
+source = "git+https://github.com/servo/webxr#3e731eac4180f739e85f8b6b9dacbc5a2015aec8"
 dependencies = [
  "android_injected_glue",
  "bindgen",
@@ -6802,7 +6803,7 @@ dependencies = [
 [[package]]
 name = "webxr-api"
 version = "0.0.1"
-source = "git+https://github.com/servo/webxr#d9ec2263b017d9c415ce35e0f4417a454564bcf2"
+source = "git+https://github.com/servo/webxr#3e731eac4180f739e85f8b6b9dacbc5a2015aec8"
 dependencies = [
  "euclid",
  "ipc-channel",