logResult[n].extra fails to serialize in worker tests

[ErichDonGubler]

Test: webgpu/cts/webgpu/web_platform/canvas/readbackFromWebGPUCanvas/dedicated.https.html?worker=dedicated&q=webgpu:web_platform,canvas,readbackFromWebGPUCanvas:offscreenCanvas,snapshot:*

This happens because the postMessage call inside of the reportTestResults function in test_worker-worker.js in WebGPU CTS loads data from result, converting result.logs into a form more amenable form for a message via toRawData. However, for this test, the extra field of one or more logs entries is populated and preserved, containing function objects as members.

Standalone CTS doesn't reproduce this by default; one needs to set the debug query parameter first:
https://gpuweb.github.io/cts/standalone/?worker=dedicated&debug=1&q=webgpu:web_platform,canvas,readbackFromWebGPUCanvas:transferToImageBitmap_unconfigured_nonzero_size:*

I presume that the Chrome hasn't run into this because…it passes most of CTS. 😅

[ErichDonGubler]

@kainino0x: If I were to file a PR for this, I think the simplest (naive) approach I might take is to serialize extra to JSON and back before sending it via postMessage. Do you think that might work?