canvas: Add OffscreenCanvas 'convertToBlob' method (#37786)

Follow the HTML speficication and add missing 'convertToBlob' method
to OffscreenCanvas interface.

https://html.spec.whatwg.org/multipage/#dom-offscreencanvas-converttoblob

Testing: Improvements in the following tests
-
html/canvas/offscreen/manual/convert-to-blob/offscreencanvas.convert.to.blob*
-
html/canvas/offscreen/manual/wide-gamut-canvas/2d.color.space.p3.convertToBlobp3.canvas.html

Fixes: #24272

Signed-off-by: Andrei Volykhin <andrei.volykhin@gmail.com>

components/script/dom/offscreencanvas.rs

@@ -3,26 +3,33 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 use std::cell::Cell;
+use std::rc::Rc;
 
+use constellation_traits::BlobImpl;
 use dom_struct::dom_struct;
 use euclid::default::Size2D;
 use js::rust::{HandleObject, HandleValue};
-use pixels::Snapshot;
+use pixels::{EncodedImageType, Snapshot};
 use script_bindings::weakref::WeakRef;
 
 use crate::canvas_context::{CanvasContext, OffscreenRenderingContext};
 use crate::dom::bindings::cell::{DomRefCell, Ref};
 use crate::dom::bindings::codegen::Bindings::OffscreenCanvasBinding::{
-    OffscreenCanvasMethods, OffscreenRenderingContext as RootedOffscreenRenderingContext,
+    ImageEncodeOptions, OffscreenCanvasMethods,
+    OffscreenRenderingContext as RootedOffscreenRenderingContext,
 };
 use crate::dom::bindings::error::{Error, Fallible};
+use crate::dom::bindings::refcounted::{Trusted, TrustedPromise};
 use crate::dom::bindings::reflector::{DomGlobal, reflect_dom_object_with_proto};
 use crate::dom::bindings::root::{Dom, DomRoot};
 use crate::dom::bindings::str::DOMString;
+use crate::dom::blob::Blob;
 use crate::dom::eventtarget::EventTarget;
 use crate::dom::globalscope::GlobalScope;
 use crate::dom::htmlcanvaselement::HTMLCanvasElement;
 use crate::dom::offscreencanvasrenderingcontext2d::OffscreenCanvasRenderingContext2D;
+use crate::dom::promise::Promise;
+use crate::realms::{AlreadyInRealm, InRealm};
 use crate::script_runtime::{CanGc, JSContext};
 
 /// <https://html.spec.whatwg.org/multipage/#offscreencanvas>
@@ -206,4 +213,71 @@ impl OffscreenCanvasMethods<crate::DomTypeHolder> for OffscreenCanvas {
             canvas.set_natural_height(value as _, can_gc)
         }
     }
+
+    /// <https://html.spec.whatwg.org/multipage/#dom-offscreencanvas-converttoblob>
+    fn ConvertToBlob(&self, options: &ImageEncodeOptions, can_gc: CanGc) -> Rc<Promise> {
+        // Step 5. Let result be a new promise object.
+        let in_realm_proof = AlreadyInRealm::assert::<crate::DomTypeHolder>();
+        let promise = Promise::new_in_current_realm(InRealm::Already(&in_realm_proof), can_gc);
+
+        // Step 2. If this's context mode is 2d and the rendering context's
+        // output bitmap's origin-clean flag is set to false, then return a
+        // promise rejected with a "SecurityError" DOMException.
+        if !self.origin_is_clean() {
+            promise.reject_error(Error::Security, can_gc);
+            return promise;
+        }
+
+        // Step 3. If this's bitmap has no pixels (i.e., either its horizontal
+        // dimension or its vertical dimension is zero), then return a promise
+        // rejected with an "IndexSizeError" DOMException.
+        if self.Width() == 0 || self.Height() == 0 {
+            promise.reject_error(Error::IndexSize, can_gc);
+            return promise;
+        }
+
+        // Step 4. Let bitmap be a copy of this's bitmap.
+        let Some(mut snapshot) = self.get_image_data() else {
+            promise.reject_error(Error::InvalidState, can_gc);
+            return promise;
+        };
+
+        // Step 7. Run these steps in parallel:
+        // Step 7.1. Let file be a serialization of bitmap as a file, with
+        // options's type and quality if present.
+        // Step 7.2. Queue a global task on the canvas blob serialization task
+        // source given global to run these steps:
+        let trusted_this = Trusted::new(self);
+        let trusted_promise = TrustedPromise::new(promise.clone());
+
+        let image_type = EncodedImageType::from(options.type_.to_string());
+        let quality = options.quality;
+
+        self.global()
+            .task_manager()
+            .canvas_blob_task_source()
+            .queue(task!(convert_to_blob: move || {
+                let this = trusted_this.root();
+                let promise = trusted_promise.root();
+
+                let mut encoded: Vec<u8> = vec![];
+
+                if snapshot.encode_for_mime_type(&image_type, quality, &mut encoded).is_err() {
+                    // Step 7.2.1. If file is null, then reject result with an
+                    // "EncodingError" DOMException.
+                    promise.reject_error(Error::Encoding, CanGc::note());
+                    return;
+                };
+
+                // Step 7.2.2. Otherwise, resolve result with a new Blob object,
+                // created in global's relevant realm, representing file.
+                let blob_impl = BlobImpl::new_from_bytes(encoded, image_type.as_mime_type());
+                let blob = Blob::new(&this.global(), blob_impl, CanGc::note());
+
+                promise.resolve_native(&blob, CanGc::note());
+            }));
+
+        // Step 8. Return result.
+        promise
+    }
 }