Auto merge of #21388 - gterzian:introduce_task_queues, r=jdm

Introduce task queues, and throttling performance timeline tasksource

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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #19997 (github issue number if applicable).

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components/script/lib.rs

@@ -5,6 +5,7 @@
 #![cfg_attr(feature = "unstable", feature(core_intrinsics))]
 #![cfg_attr(feature = "unstable", feature(on_unimplemented))]
 #![feature(const_fn)]
+#![feature(drain_filter)]
 #![feature(mpsc_select)]
 #![feature(plugin)]
 #![feature(try_from)]
@@ -123,6 +124,7 @@ pub mod script_thread;
 mod serviceworker_manager;
 mod serviceworkerjob;
 mod stylesheet_loader;
+mod task_queue;
 mod task_source;
 pub mod test;
 pub mod textinput;