constellation: notify embedder when events are hit-tested to browsers (#30841)

* constellation: notify embedder when events are hit-tested to browsers

* fix compile error in libsimpleservo

* impl From<&CompositorEvent> for CompositorEventVariant

* remove msg temporaries in Constellation::forward_event

* use single wildcard arm in EventDelivered case in handle_servo_events

components/shared/embedder/lib.rs

@@ -208,6 +208,21 @@ pub enum EmbedderMsg {
     OnDevtoolsStarted(Result<u16, ()>, String),
     /// Compositing done, but external code needs to present.
     ReadyToPresent,
+    /// The given event was delivered to a pipeline in the given browser.
+    EventDelivered(CompositorEventVariant),
+}
+
+/// The variant of CompositorEvent that was delivered to a pipeline.
+#[derive(Debug, Deserialize, Serialize)]
+pub enum CompositorEventVariant {
+    ResizeEvent,
+    MouseButtonEvent,
+    MouseMoveEvent,
+    TouchEvent,
+    WheelEvent,
+    KeyboardEvent,
+    CompositionEvent,
+    IMEDismissedEvent,
 }
 
 impl Debug for EmbedderMsg {
@@ -245,6 +260,7 @@ impl Debug for EmbedderMsg {
             EmbedderMsg::OnDevtoolsStarted(..) => write!(f, "OnDevtoolsStarted"),
             EmbedderMsg::ShowContextMenu(..) => write!(f, "ShowContextMenu"),
             EmbedderMsg::ReadyToPresent => write!(f, "ReadyToPresent"),
+            EmbedderMsg::EventDelivered(..) => write!(f, "HitTestedEvent"),
         }
     }
 }

components/shared/script/lib.rs

@@ -27,7 +27,7 @@ use canvas_traits::webgl::WebGLPipeline;
 use compositor::ScrollTreeNodeId;
 use crossbeam_channel::{Receiver, RecvTimeoutError, Sender};
 use devtools_traits::{DevtoolScriptControlMsg, ScriptToDevtoolsControlMsg, WorkerId};
-use embedder_traits::Cursor;
+use embedder_traits::{CompositorEventVariant, Cursor};
 use euclid::default::Point2D;
 use euclid::{Length, Rect, Scale, Size2D, UnknownUnit, Vector2D};
 use gfx_traits::Epoch;
@@ -571,6 +571,21 @@ pub enum CompositorEvent {
     IMEDismissedEvent,
 }
 
+impl From<&CompositorEvent> for CompositorEventVariant {
+    fn from(value: &CompositorEvent) -> Self {
+        match value {
+            CompositorEvent::ResizeEvent(..) => CompositorEventVariant::ResizeEvent,
+            CompositorEvent::MouseButtonEvent(..) => CompositorEventVariant::MouseButtonEvent,
+            CompositorEvent::MouseMoveEvent(..) => CompositorEventVariant::MouseMoveEvent,
+            CompositorEvent::TouchEvent(..) => CompositorEventVariant::TouchEvent,
+            CompositorEvent::WheelEvent(..) => CompositorEventVariant::WheelEvent,
+            CompositorEvent::KeyboardEvent(..) => CompositorEventVariant::KeyboardEvent,
+            CompositorEvent::CompositionEvent(..) => CompositorEventVariant::CompositionEvent,
+            CompositorEvent::IMEDismissedEvent => CompositorEventVariant::IMEDismissedEvent,
+        }
+    }
+}
+
 /// Requests a TimerEvent-Message be sent after the given duration.
 #[derive(Debug, Deserialize, Serialize)]
 pub struct TimerEventRequest(