Implement initial version of ReportingObserver (#37905)

The specification moved around lately with how it defines its reports
and report bodies. They became dictionaries, but are currently missing
some fields [1].

Most tests won't be passing yet, since the `Reporting-Endpoints` header
isn't used yet. In fact, the specification leaves it up to the browser
to figure out when to run this task [2]. I am not sure if there some
background scheduling we can do here.

Confirmed with content-security-policy/reporting-api/
report-to-directive-allowed-in-meta.https.sub.html that the callback is
invoked. The test doesn't pass, since
the `describe_scripted_caller` is empty for HTML elements. Thus the
`source_file` is empty, whereas it should be equivalent to the current
document URL.

Part of #37328

Signed-off-by: Tim van der Lippe <tvanderlippe@gmail.com>

[1]: https://github.com/w3c/reporting/issues/286
[2]: https://w3c.github.io/reporting/#report-delivery

components/script/dom/workerglobalscope.rs

@@ -36,6 +36,7 @@ use crate::dom::bindings::cell::{DomRefCell, Ref};
 use crate::dom::bindings::codegen::Bindings::ImageBitmapBinding::{
     ImageBitmapOptions, ImageBitmapSource,
 };
+use crate::dom::bindings::codegen::Bindings::ReportingObserverBinding::Report;
 use crate::dom::bindings::codegen::Bindings::RequestBinding::RequestInit;
 use crate::dom::bindings::codegen::Bindings::VoidFunctionBinding::VoidFunction;
 use crate::dom::bindings::codegen::Bindings::WorkerBinding::WorkerType;
@@ -56,6 +57,7 @@ use crate::dom::globalscope::GlobalScope;
 use crate::dom::idbfactory::IDBFactory;
 use crate::dom::performance::Performance;
 use crate::dom::promise::Promise;
+use crate::dom::reportingobserver::ReportingObserver;
 use crate::dom::trustedscripturl::TrustedScriptURL;
 use crate::dom::trustedtypepolicyfactory::TrustedTypePolicyFactory;
 use crate::dom::types::ImageBitmap;
@@ -139,6 +141,12 @@ pub(crate) struct WorkerGlobalScope {
 
     #[no_trace]
     insecure_requests_policy: InsecureRequestsPolicy,
+
+    /// <https://w3c.github.io/reporting/#windoworworkerglobalscope-registered-reporting-observer-list>
+    reporting_observer_list: DomRefCell<Vec<DomRoot<ReportingObserver>>>,
+
+    /// <https://w3c.github.io/reporting/#windoworworkerglobalscope-reports>
+    report_list: DomRefCell<Vec<Report>>,
 }
 
 impl WorkerGlobalScope {
@@ -196,6 +204,8 @@ impl WorkerGlobalScope {
             timer_scheduler: RefCell::default(),
             insecure_requests_policy,
             trusted_types: Default::default(),
+            reporting_observer_list: Default::default(),
+            report_list: Default::default(),
         }
     }
 
@@ -259,6 +269,35 @@ impl WorkerGlobalScope {
         self.policy_container.borrow_mut().set_csp_list(csp_list);
     }
 
+    pub(crate) fn append_reporting_observer(&self, reporting_observer: DomRoot<ReportingObserver>) {
+        self.reporting_observer_list
+            .borrow_mut()
+            .push(reporting_observer);
+    }
+
+    pub(crate) fn remove_reporting_observer(&self, reporting_observer: &ReportingObserver) {
+        if let Some(index) = self
+            .reporting_observer_list
+            .borrow()
+            .iter()
+            .position(|observer| &**observer == reporting_observer)
+        {
+            self.reporting_observer_list.borrow_mut().remove(index);
+        }
+    }
+
+    pub(crate) fn registered_reporting_observers(&self) -> Vec<DomRoot<ReportingObserver>> {
+        self.reporting_observer_list.borrow().clone()
+    }
+
+    pub(crate) fn append_report(&self, report: Report) {
+        self.report_list.borrow_mut().push(report);
+    }
+
+    pub(crate) fn buffered_reports(&self) -> Vec<Report> {
+        self.report_list.borrow().clone()
+    }
+
     /// Get a mutable reference to the [`TimerScheduler`] for this [`ServiceWorkerGlobalScope`].
     pub(crate) fn timer_scheduler(&self) -> RefMut<TimerScheduler> {
         self.timer_scheduler.borrow_mut()