Auto merge of #17150 - asajeffrey:script-paint-worklets-plumbing, r=jdm

Implemented the plumbing for paint worklets

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This PR implements the plumbing for paint worklets:

* Adding CSS values for paint worklets.
* Implementing a skeleton for the `PaintWorkletGlobalScope` webidl.
* Implementing an executor for paint worklet tasks, and passing it from script to layout.
* Building the display list items for paint worklet images.

This PR does not implement registering or calling paint worklets in JS.

Before it merges, this PR needs a reftest added for basic paint worklet functionality.

---
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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [ ] There are tests for these changes

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1 files changed, 17 insertions, 0 deletions

diff --git a/components/script/dom/window.rs b/components/script/dom/window.rs
index fc793c206c4..e627721bd05 100644
--- a/components/script/dom/window.rs
+++ b/components/script/dom/window.rs
@@ -51,6 +51,7 @@ use dom::storage::Storage;
 use dom::testrunner::TestRunner;
 use dom::windowproxy::WindowProxy;
 use dom::worklet::Worklet;
+use dom::workletglobalscope::WorkletGlobalScopeType;
 use dom_struct::dom_struct;
 use euclid::{Point2D, Rect, Size2D};
 use fetch;
@@ -279,6 +280,8 @@ pub struct Window {
 
     /// Worklets
     test_worklet: MutNullableJS<Worklet>,
+    /// https://drafts.css-houdini.org/css-paint-api-1/#paint-worklet
+    paint_worklet: MutNullableJS<Worklet>,
 }
 
 impl Window {
@@ -373,6 +376,14 @@ impl Window {
         self.webvr_thread.clone()
     }
 
+    fn new_paint_worklet(&self) -> Root<Worklet> {
+        debug!("Creating new paint worklet.");
+        let worklet = Worklet::new(self, WorkletGlobalScopeType::Paint);
+        let executor = Arc::new(worklet.executor());
+        let _ = self.layout_chan.send(Msg::SetPaintWorkletExecutor(executor));
+        worklet
+    }
+
     pub fn permission_state_invocation_results(&self) -> &DOMRefCell<HashMap<String, PermissionState>> {
         &self.permission_state_invocation_results
     }
@@ -1011,6 +1022,11 @@ impl WindowMethods for Window {
         fetch::Fetch(&self.upcast(), input, init)
     }
 
+    // https://drafts.css-houdini.org/css-paint-api-1/#paint-worklet
+    fn PaintWorklet(&self) -> Root<Worklet> {
+        self.paint_worklet.or_init(|| self.new_paint_worklet())
+    }
+
     fn TestRunner(&self) -> Root<TestRunner> {
         self.test_runner.or_init(|| TestRunner::new(self.upcast()))
     }
@@ -1856,6 +1872,7 @@ impl Window {
             pending_layout_images: DOMRefCell::new(HashMap::new()),
             unminified_js_dir: DOMRefCell::new(None),
             test_worklet: Default::default(),
+            paint_worklet: Default::default(),
         };
 
         unsafe {