Auto merge of #20329 - gterzian:before_unload, r=cbrewster

Implement beforeunload event and infrastructure

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Implementation of:
1. https://html.spec.whatwg.org/multipage/#prompt-to-unload-a-document, and
2. https://html.spec.whatwg.org/multipage/#unload-a-document
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- [ ] `./mach build -d` does not report any errors
- [ ] `./mach test-tidy` does not report any errors
- [ ] These changes fix #10787 and fix #20485 and fix #20588 and fix #20496 (github issue number if applicable).

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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____

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1 files changed, 10 insertions, 0 deletions

diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index 6ee0ec46d33..613918f6a76 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -1157,6 +1157,7 @@ impl ScriptThread {
                     AttachLayout(ref new_layout_info) => Some(new_layout_info.new_pipeline_id),
                     Resize(id, ..) => Some(id),
                     ResizeInactive(id, ..) => Some(id),
+                    UnloadDocument(id) => Some(id),
                     ExitPipeline(id, ..) => Some(id),
                     ExitScriptThread => None,
                     SendEvent(id, ..) => Some(id),
@@ -1275,6 +1276,8 @@ impl ScriptThread {
             },
             ConstellationControlMsg::Navigate(parent_pipeline_id, browsing_context_id, load_data, replace) =>
                 self.handle_navigate(parent_pipeline_id, Some(browsing_context_id), load_data, replace),
+            ConstellationControlMsg::UnloadDocument(pipeline_id) =>
+                self.handle_unload_document(pipeline_id),
             ConstellationControlMsg::SendEvent(id, event) =>
                 self.handle_event(id, event),
             ConstellationControlMsg::ResizeInactive(id, new_size) =>
@@ -1668,6 +1671,13 @@ impl ScriptThread {
         }
     }
 
+    fn handle_unload_document(&self, pipeline_id: PipelineId) {
+        let document = self.documents.borrow().find_document(pipeline_id);
+        if let Some(document) = document {
+            document.unload(false, false);
+        }
+    }
+
     fn handle_update_pipeline_id(&self,
                                  parent_pipeline_id: PipelineId,
                                  browsing_context_id: BrowsingContextId,