servo: Merge #6677 - Make iframes block the enclosing document's load event (from jdm:iframeblockonload); r=Ms2ger

It occurs to me as I write this that this doesn't handle the case of removing the iframe from the document before it's finished loading. Consider this an early feedback release!

Source-Repo: https://github.com/servo/servo
Source-Revision: a31f31e81977be5215f31851885e8ab46890c556

servo/components/script_traits/lib.rs

@@ -142,7 +142,7 @@ pub enum ConstellationControlMsg {
         /// The pipeline that has been marked as loaded.
         target: PipelineId,
         /// The pipeline that contains a frame loading the target pipeline.
-        parent: PipelineId
+        parent: PipelineId,
     },
     /// Notifies a parent frame that one of its child frames is now active.
     FramedContentChanged(PipelineId, SubpageId),