Changed performance interface's timing to an attribute

[bcamp]

---

• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• These changes fix #23330 (GitHub issue number if applicable)

• There are tests for these changes OR
• These changes do not require tests because ___

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This change is 

[highfive]

Thanks for the pull request, and welcome! The Servo team is excited to review your changes, and you should hear from @Manishearth (or someone else) soon.

[highfive]

Heads up! This PR modifies the following files:

• @asajeffrey: components/script/dom/webidls/Performance.webidl
• @KiChjang: components/script/dom/webidls/Performance.webidl

[highfive]

Warning

• These commits modify script code, but no tests are modified. Please consider adding a test!

[jdm]

@bors-servo try=wpt

[bors-servo]

⌛ Trying commit 58557e0 with merge 7a64745...

[bors-servo]

💔 Test failed - linux-rel-css

[jdm]

./mach test-wpt tests/wpt/mozilla/window_performance.html is now panicking when calling Performance::Timing.

[jdm]

More specifically, the panic occurs because in this code there is no navigation timing entry that has been reported when a page like this is loaded:

<script>
console.log(navigation.timing)
</script>

This occurs because we only register performance entries when a response is complete, rather than when the first bytes are received. I think we need to update all of the resource timing code to submit twice - when the first bytes are received, and then update the existing entry when all of the final timings are available.

We could:

• add a ResourceFetchTiming argument to the Result passed in process_response
• call submit_resource_timing after creating the document parser
• make Performance::queue_entries return the index of the added performance entry in self.entries
• add a update_entry method to Performance that accepts an index and a &PerformanceEntry value and overwrites the corresponding entry in self.entries
• call the new update_entry API from process_response_eof

[bcamp]

Just updating to say that I'm working on an implementation of your proposed solution. Should have an update some time this week.

[jdm]

@bcamp Are you still working on this? :)

[bcamp]

My bad, this completely slipped my mind as work and school have been consuming my time. I don't think I'll be able to get to this in a timely manner (as already displayed).