ElementTiming span timestamp uses render time

[nikolovlazar]

ElementTiming spans are being emitted with sentry.span_start_time_source: "render-time", and start_timestamp/timestamp set to the render time value (e.g. 0.912) instead of a proper timestamp.

Example span payload:

{
  "data": {
    "sentry.origin": "auto.ui.browser.elementtiming",
    "sentry.op": "ui.elementtiming",
    "sentry.source": "component",
    "sentry.span_start_time_source": "render-time",
    "sentry.transaction_name": "/",
    "element.id": "",
    "element.type": "h2",
    "element.render_time": 912,
    "element.load_time": 0,
    "element.identifier": "favorites-section",
    "element.paint_type": "text-paint"
  },
  "description": "element[favorites-section]",
  "op": "ui.elementtiming",
  "parent_span_id": "be8a7d8fcb718936",
  "span_id": "ba9779cdd4eb7d9c",
  "start_timestamp": 0.912,     <---------- wrong
  "timestamp": 0.912,           <---------- wrong
  "trace_id": "615676074261b7e41169a264f66ad4e5",
  "origin": "auto.ui.browser.elementtiming"
}

[linear]

JS-1678

[nikolovlazar]

just for giggles, @logaretm and I tried to add a 1x1 background-image to a section element that wasn't being reported, and it actually worked:

      {
        "data": {
          "sentry.origin": "auto.ui.browser.elementtiming",
          "sentry.op": "ui.elementtiming",
          "sentry.source": "component",
          "sentry.span_start_time_source": "load-time",
          "sentry.transaction_name": "/",
          "element.id": "",
          "element.type": "section",
          "element.size": "1x1",
          "element.render_time": 636,
          "element.load_time": 602.8999999985099,
          "element.url": "data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAEAAAABCAQAAAC1HAwCAAAAC0lEQVR42mNkYAAAAAYAAjCB0C8AAA",
          "element.identifier": "favorites-section",
          "element.paint_type": "image-paint"
        },
        "description": "element[favorites-section]",
        "op": "ui.elementtiming",
        "parent_span_id": "a0e6ccf9b295adca",
        "span_id": "82011063de8fd14f",
        "start_timestamp": 0.6028999999985099,
        "timestamp": 0.636,
        "trace_id": "ab6699a03db44770b7b4ba4274ead1fd",
        "origin": "auto.ui.browser.elementtiming"
      },

we fooled Chrome into reporting timing for an element that didn't report initially 😁