Iframes incorrectly do not fire a load event if the site inside the iframe fails to load

[skyz1]

Summary

When the content of an iframe fails to load, the warning icon on the error page does not load. The load event is consequently not fired.

This issue was introduced in #2162, specifically d03f887. The request itself is successful, but the handlers for the success case are not called. The cause could be the implementation of readable_stream_pipe_to, but I'm not sure.

Operating system

macOS

Steps to reproduce

1. Open http://wpt.live/x-frame-options/get-decode-split.html

Expected behavior

The warning icon shows up on the error pages in the iframes and the tests pass.

Actual behavior

The warning icon does not load and the test times out, because the load event does not fire.

URL for a reduced test case

N/A

HTML/SVG/etc. source for a reduced test case

<iframe src="./missing-file"></iframe>

Log output and (if possible) backtrace

N/A

Screenshots or screen recordings

No response

Build flags or config settings

No response

Contribute a patch?

• I’ll contribute a patch for this myself.

[shannonbooth]

Likely related (at least tangentially) to #2893