Fast page assets no longer get a span.
A page load emits one resourceFetch span per stylesheet, font and chunk — seven of every eleven page-load spans on our own app, and on a warm cache the same seven near-instant hits recorded again on every visit by every visitor. documentLoad already reports that the page took 1.6 seconds; an asset span earns its storage when it says which font that was.
assetFloorMs (default 100) drops fast, successful asset spans as the batch leaves the browser. An asset that failed is always kept, however fast it failed — that is the case worth looking at, and Resource Timing leaves no status code to find it by afterwards. A span that isn't recognisably a timed asset is never dropped.
assetFloorMs: 0 restores 0.2.1 behaviour. No other API change.