Auto merge of #16506 - cbrewster:about_chaos, r=asajeffrey

Make non-initial about:blank loads async

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- [X] `./mach build -d` does not report any errors
- [X] `./mach test-tidy` does not report any errors
- [X] These changes fix #14856 (github issue number if applicable).

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- [ ] There are tests for these changes OR
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components/script/layout_wrapper.rs

@@ -44,7 +44,7 @@ use dom::node::{LayoutNodeHelpers, Node};
 use dom::text::Text;
 use gfx_traits::ByteIndex;
 use html5ever::{LocalName, Namespace};
-use msg::constellation_msg::PipelineId;
+use msg::constellation_msg::{FrameId, PipelineId};
 use range::Range;
 use script_layout_interface::{HTMLCanvasData, LayoutNodeType, SVGSVGData, TrustedNodeAddress};
 use script_layout_interface::{OpaqueStyleAndLayoutData, PartialPersistentLayoutData};
@@ -908,6 +908,11 @@ impl<'ln> ThreadSafeLayoutNode for ServoThreadSafeLayoutNode<'ln> {
         this.svg_data()
     }
 
+    fn iframe_frame_id(&self) -> FrameId {
+        let this = unsafe { self.get_jsmanaged() };
+        this.iframe_frame_id()
+    }
+
     fn iframe_pipeline_id(&self) -> PipelineId {
         let this = unsafe { self.get_jsmanaged() };
         this.iframe_pipeline_id()