script: Cache the current favicon on the document (#39575)

This allows us to notify the embedder when navigating back and forth.

Testing: Manual testing following the steps in issue #39529 
Fixes: https://github.com/servo/servo/issues/39529

Signed-off-by: webbeef <me@webbeef.org>

components/script/dom/document.rs

@@ -26,7 +26,9 @@ use cssparser::match_ignore_ascii_case;
 use data_url::mime::Mime;
 use devtools_traits::ScriptToDevtoolsControlMsg;
 use dom_struct::dom_struct;
-use embedder_traits::{AllowOrDeny, AnimationState, EmbedderMsg, FocusSequenceNumber, LoadStatus};
+use embedder_traits::{
+    AllowOrDeny, AnimationState, EmbedderMsg, FocusSequenceNumber, Image, LoadStatus,
+};
 use encoding_rs::{Encoding, UTF_8};
 use euclid::Point2D;
 use euclid::default::{Rect, Size2D};
@@ -576,6 +578,10 @@ pub(crate) struct Document {
     #[ignore_malloc_size_of = "type from external crate"]
     /// <https://html.spec.whatwg.org/multipage/#active-sandboxing-flag-set>,
     active_sandboxing_flag_set: Cell<SandboxingFlagSet>,
+    /// The cached favicon for that document.
+    #[no_trace]
+    #[ignore_malloc_size_of = "TODO: unimplemented on Image"]
+    favicon: RefCell<Option<Image>>,
 }
 
 #[allow(non_snake_case)]
@@ -762,6 +768,7 @@ impl Document {
         }
 
         self.title_changed();
+        self.notify_embedder_favicon();
         self.dirty_all_nodes();
         self.window().resume(can_gc);
         media.resume(&client_context_id);
@@ -3495,6 +3502,7 @@ impl Document {
             current_canvas_epoch: RefCell::new(Epoch(0)),
             custom_element_reaction_stack,
             active_sandboxing_flag_set: Cell::new(SandboxingFlagSet::empty()),
+            favicon: RefCell::new(None),
         }
     }
 
@@ -4478,6 +4486,17 @@ impl Document {
             .scrolling_box_query(None, flags)
             .expect("We should always have a ScrollingBox for the Viewport")
     }
+
+    pub(crate) fn notify_embedder_favicon(&self) {
+        if let Some(ref image) = *self.favicon.borrow() {
+            self.send_to_embedder(EmbedderMsg::NewFavicon(self.webview_id(), image.clone()));
+        }
+    }
+
+    pub(crate) fn set_favicon(&self, favicon: Image) {
+        *self.favicon.borrow_mut() = Some(favicon);
+        self.notify_embedder_favicon();
+    }
 }
 
 #[allow(non_snake_case)]

components/script/dom/html/htmllinkelement.rs

@@ -7,7 +7,6 @@ use std::cell::Cell;
 use std::default::Default;
 
 use dom_struct::dom_struct;
-use embedder_traits::EmbedderMsg;
 use html5ever::{LocalName, Prefix, local_name, ns};
 use ipc_channel::ipc::IpcSender;
 use js::rust::HandleObject;
@@ -726,6 +725,7 @@ impl HTMLLinkElement {
     fn process_favicon_response(&self, image: Image) {
         // TODO: Include the size attribute here
         let window = self.owner_window();
+        let document = self.owner_document();
 
         let send_rasterized_favicon_to_embedder = |raster_image: &pixels::RasterImage| {
             // Let's not worry about animated favicons...
@@ -746,7 +746,7 @@ impl HTMLLinkElement {
                 raster_image.frames[0].byte_range.clone(),
                 format,
             );
-            window.send_to_embedder(EmbedderMsg::NewFavicon(window.webview_id(), embedder_image));
+            document.set_favicon(embedder_image);
         };
 
         match image {