Serializing childrenonly
Rebased from #17896.
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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#14975 (github issue number if applicable).
- [x] There are tests for these changes
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Make cross-origin canvas drawing tests use a same-origin redirect.
These tests either pass or maintain existing known failures in Firefox and Chrome, and expose the problem in our current implementation that #15887 is addressing.
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Don't create a new XHR until the previous one is complete.
This test often times out when run under rr, because the event loop gets flooded with timer events that initiate XHRs before the previous XHR has completed. Additionally, we're running the event handler up to three times per XHR, which is just silly.
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implement structured clone callbacks - support Blob cloning
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1. Implement stubs for structured clone callbacks.
2. Support Blob cloning.
Partial implementation of https://developer.mozilla.org/en-US/docs/Web/API/Web_Workers_API/Structured_clone_algorithm
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- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix#15021 (github issue number if applicable).
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- [ ] There are tests for these changes OR
- [ ] These changes do not require tests because _____
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