servo: Merge #6175 - Embedding: revenge of cargo (from zmike:embedding-REVENGE_OF_CARGO); r=larsbergstrom

Adds a bunch more embedding interfaces/callbacks/functionality

@larsbergstrom

Source-Repo: https://github.com/servo/servo
Source-Revision: 94ebfe81e454ca6dd68210b4475b4091e836dd1a

servo/components/script/script_task.rs

@@ -960,7 +960,7 @@ impl ScriptTask {
         self.chan.send(ScriptMsg::RunnableMsg(handler)).unwrap();
 
         let ConstellationChan(ref chan) = self.constellation_chan;
-        chan.send(ConstellationMsg::LoadComplete).unwrap();
+        chan.send(ConstellationMsg::LoadComplete(pipeline)).unwrap();
     }
 
     /// Handles a timer that fired.