Implement non-XR Gamepad discovery and input (#31200)

* Create embedder event to send to constellation

* Handle gamepad message in constellation, send to script thread

* Handle GamepadEvent in script thread and dispatch event to document

* Add missing Clones, fix event

* Add gamepad task source

* Adjust GamepadIndex type, remove unused imports

* Add internal getter for gamepads list

* Update gamepad new methods

* Handle gamepad connect and disconnect events

* Proto will be none, no need for HandleObject

* Initialize buttons and axes to standard mapping

* Adjust update type index types

* Update GamepadButton update function

* Adjust Gamepad mapping comments to match spec, add update logic

* Amend comment

* Update button and axis inputs on Updated event

* Add GilRs as gamepad backend in servoshell

* Add spec links, queue gamepad updates on task source

* ./mach fmt

* Fix comment length

* Split out button init, update spec comments

* Move gamepad event handling from document to global

* Map and normalize axes/button values

* Use std::time for gamepad timestamp

* Adjust gamepad handling in event loop

* Move button press/touch check into map+normalize function

- Small change but is more in line with spec

* ./mach fmt

* Update comment spec links and warning messages

* Doc comments -> regular comments

* Add window event handlers for gamepad connect/disconnect

* Adjust gamepad disconnect behavior

* Add missing TODO's, adjust gamepad/gamepadbutton list methods and formatting

* Update button handling from gilrs, add comments

* Enable gamepad pref during WPT tests and update expectations

* Update WPT expectations in meta-legacy-layout

components/script/task_source/gamepad.rs

@@ -0,0 +1,47 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+use std::fmt;
+use std::result::Result;
+
+use msg::constellation_msg::PipelineId;
+
+use crate::script_runtime::{CommonScriptMsg, ScriptChan, ScriptThreadEventCategory};
+use crate::task::{TaskCanceller, TaskOnce};
+use crate::task_source::{TaskSource, TaskSourceName};
+
+#[derive(JSTraceable)]
+pub struct GamepadTaskSource(
+    pub Box<dyn ScriptChan + Send + 'static>,
+    #[no_trace] pub PipelineId,
+);
+
+impl Clone for GamepadTaskSource {
+    fn clone(&self) -> GamepadTaskSource {
+        GamepadTaskSource(self.0.clone(), self.1.clone())
+    }
+}
+
+impl fmt::Debug for GamepadTaskSource {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(f, "GamepadTaskSource(...)")
+    }
+}
+
+impl TaskSource for GamepadTaskSource {
+    const NAME: TaskSourceName = TaskSourceName::Gamepad;
+
+    fn queue_with_canceller<T>(&self, task: T, canceller: &TaskCanceller) -> Result<(), ()>
+    where
+        T: TaskOnce + 'static,
+    {
+        let msg = CommonScriptMsg::Task(
+            ScriptThreadEventCategory::InputEvent,
+            Box::new(canceller.wrap_task(task)),
+            Some(self.1),
+            GamepadTaskSource::NAME,
+        );
+        self.0.send(msg).map_err(|_| ())
+    }
+}

components/script/task_source/mod.rs

@@ -4,6 +4,7 @@
 
 pub mod dom_manipulation;
 pub mod file_reading;
+pub mod gamepad;
 pub mod history_traversal;
 pub mod media_element;
 pub mod networking;
@@ -38,6 +39,8 @@ pub enum TaskSourceName {
     MediaElement,
     Websocket,
     Timer,
+    /// <https://www.w3.org/TR/gamepad/#dfn-gamepad-task-source>
+    Gamepad,
 }
 
 impl TaskSourceName {