Auto merge of #18704 - mrobinson:wr-hit-testing, r=jdm,glennw,mbrubeck

Switch to using WebRender hit testing

This trades quite a bit of complicated code in Servo for few more
messages and a significant performance improvement. In particular,
WebRender can search the entire display list at once instead of
ping-ponging down the pipeline tree. This allows us to send mouse
events to the correct pipeline immediately.

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

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they should not change behavior.

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components/constellation/constellation.rs

@@ -1082,6 +1082,12 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
                 debug!("constellation got {:?} WebVR events", events.len());
                 self.handle_webvr_events(pipeline_ids, events);
             }
+            FromCompositorMsg::ForwardEvent(destination_pipeline_id, event) => {
+                self.forward_event(destination_pipeline_id, event);
+            }
+            FromCompositorMsg::SetCursor(cursor) => {
+                self.handle_set_cursor_msg(cursor)
+            }
         }
     }
 
@@ -1175,15 +1181,8 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
                 debug!("constellation got focus message");
                 self.handle_focus_msg(source_pipeline_id);
             }
-            FromScriptMsg::ForwardEvent(dest_id, event) => {
-                let msg = ConstellationControlMsg::SendEvent(dest_id, event);
-                let result = match self.pipelines.get(&dest_id) {
-                    None => { debug!("Pipeline {:?} got event after closure.", dest_id); return; }
-                    Some(pipeline) => pipeline.event_loop.send(msg),
-                };
-                if let Err(e) = result {
-                    self.handle_send_error(dest_id, e);
-                }
+            FromScriptMsg::ForwardEvent(destination_pipeline_id, event) => {
+                self.forward_event(destination_pipeline_id, event);
             }
             FromScriptMsg::GetClipboardContents(sender) => {
                 let contents = match self.clipboard_ctx {
@@ -1250,13 +1249,6 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
                 debug!("constellation got Alert message");
                 self.handle_alert(source_top_ctx_id, message, sender);
             }
-
-            FromScriptMsg::ScrollFragmentPoint(scroll_root_id, point, smooth) => {
-                self.compositor_proxy.send(ToCompositorMsg::ScrollFragmentPoint(scroll_root_id,
-                                                                                point,
-                                                                                smooth));
-            }
-
             FromScriptMsg::GetClientWindow(send) => {
                 self.embedder_proxy.send(EmbedderMsg::GetClientWindow(source_top_ctx_id, send));
             }
@@ -1592,6 +1584,20 @@ impl<Message, LTF, STF> Constellation<Message, LTF, STF>
         }
     }
 
+    fn forward_event(&mut self, destination_pipeline_id: PipelineId, event: CompositorEvent) {
+        let msg = ConstellationControlMsg::SendEvent(destination_pipeline_id, event);
+        let result = match self.pipelines.get(&destination_pipeline_id) {
+            None => {
+                debug!("Pipeline {:?} got event after closure.", destination_pipeline_id);
+                return;
+            }
+            Some(pipeline) => pipeline.event_loop.send(msg),
+        };
+        if let Err(e) = result {
+            self.handle_send_error(destination_pipeline_id, e);
+        }
+    }
+
     fn handle_new_top_level_browsing_context(&mut self, url: ServoUrl, reply: IpcSender<TopLevelBrowsingContextId>) {
         let window_size = self.window_size.initial_viewport;
         let pipeline_id = PipelineId::new();