Auto merge of #16814 - asajeffrey:script-worklets, r=jdm

Implement Houdini worklets

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This PR implements the current draft Houdini Worklets specification (https://drafts.css-houdini.org/worklets/).

The implementation is intended to provide a responsive environment for worklet execution, and in particular to ensure that the primary worklet executor does not garbage collect, and does not block loading module code. The implementation does this by providing a thread pool, and performing GC and module loading in a backup thread, not in the primary thread.

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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 fix #16206
- [x] There are tests for these changes

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1 files changed, 5 insertions, 0 deletions

diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index 65d1a591adc..097f136e29c 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -49,6 +49,7 @@ use dom::screen::Screen;
 use dom::storage::Storage;
 use dom::testrunner::TestRunner;
 use dom::windowproxy::WindowProxy;
+use dom::worklet::Worklet;
 use dom_struct::dom_struct;
 use euclid::{Point2D, Rect, Size2D};
 use fetch;
@@ -273,6 +274,9 @@ pub struct Window {
     /// Directory to store unminified scripts for this window if unminify-js
     /// opt is enabled.
     unminified_js_dir: DOMRefCell<Option<String>>,
+
+    /// Worklets
+    test_worklet: MutNullableJS<Worklet>,
 }
 
 impl Window {
@@ -1830,6 +1834,7 @@ impl Window {
             permission_state_invocation_results: DOMRefCell::new(HashMap::new()),
             pending_layout_images: DOMRefCell::new(HashMap::new()),
             unminified_js_dir: DOMRefCell::new(None),
+            test_worklet: Default::default(),
         };
 
         unsafe {