add handling for favicon link elements

fixes #6166

components/compositing/compositor.rs

@@ -454,6 +454,10 @@ impl<Window: WindowMethods> IOCompositor<Window> {
                 self.composite_if_necessary(CompositingReason::Headless);
             }
 
+            (Msg::NewFavicon(url), ShutdownState::NotShuttingDown) => {
+                self.window.set_favicon(url);
+            }
+
             // When we are shutting_down, we need to avoid performing operations
             // such as Paint that may crash because we have begun tearing down
             // the rest of our resources.

components/compositing/compositor_task.rs

@@ -180,6 +180,8 @@ pub enum Msg {
     ViewportConstrained(PipelineId, ViewportConstraints),
     /// A reply to the compositor asking if the output image is stable.
     IsReadyToSaveImageReply(bool),
+    /// A favicon was detected
+    NewFavicon(Url),
 }
 
 impl Debug for Msg {
@@ -206,6 +208,7 @@ impl Debug for Msg {
             Msg::PaintTaskExited(..) => write!(f, "PaintTaskExited"),
             Msg::ViewportConstrained(..) => write!(f, "ViewportConstrained"),
             Msg::IsReadyToSaveImageReply(..) => write!(f, "IsReadyToSaveImageReply"),
+            Msg::NewFavicon(..) => write!(f, "NewFavicon"),
         }
     }
 }

components/compositing/constellation.rs

@@ -468,6 +468,10 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                 debug!("constellation got remove iframe message");
                 self.handle_remove_iframe_msg(containing_pipeline_id, subpage_id);
             }
+            ConstellationMsg::NewFavicon(url) => {
+                debug!("constellation got new favicon message");
+                self.compositor_proxy.send(CompositorMsg::NewFavicon(url));
+            }
         }
         true
     }

components/compositing/headless.rs

@@ -109,6 +109,7 @@ impl CompositorEventListener for NullCompositor {
             Msg::CreatePng(..) |
             Msg::PaintTaskExited(..) |
             Msg::IsReadyToSaveImageReply(..) => {}
+            Msg::NewFavicon(..) => {}
         }
         true
     }

components/compositing/windowing.rs

@@ -138,4 +138,7 @@ pub trait WindowMethods {
 
     /// Does this window support a clipboard
     fn supports_clipboard(&self) -> bool;
+
+    /// Add a favicon
+    fn set_favicon(&self, url: Url);
 }