LoAF Summary attribution information

[tunetheweb]

Fixes #559

Includes object like this:

"longAnimationFrameSummary": {
    "numLongAnimationFrames": 3,
    "numIntersectingScripts": 9,
    "slowestScript": {
      "entry": // Not Shown,
      "subpart": "processingDuration",
      "intersectingDuration": 395,
      "totalDuration": 395,
      "compileDuration": 0,
      "executionDuration": 395,
      "forcedStyleAndLayoutDuration": 144,
      "pauseDuration": 0,
      "invokerType": "event-listener",
      "invoker": "BUTTON.onclick",
      "sourceURL": "",
      "sourceFunctionName": "",
      "sourceCharPosition": -1,
    },
    "totalDurationsPerSubpart": {
        "inputDelay": {
            "user-callback": 28,
            "event-listener": 185
        },
        "processingDuration": {
            "event-listener": 434
        }
    },
    "totalForcedStyleAndLayoutDuration": 144,
    "totalNonForcedStyleAndLayoutDuration": 3144099.700000003,
    "totalScriptDuration": 647
}

[rviscomi]

Thanks Barry! Left a few comments.

[rviscomi]

I think there's an open question whether we should only be taking the blocking/intersecting portion of all duration metrics. WDYT?

[tunetheweb]

Unfortunately we can't for forced style and layout since we don't have the timings LoAF. Maybe that's a good reason to keep this simple and just take it for all intersecting scripts (which is what it does currently)?

[brendankenny]

incidentally, it seems like we're leaning subparts, not phases for LCP, so we might want to do the same thing here (or object quickly on the LCP side of things :)

[tunetheweb]

incidentally, it seems like we're leaning subparts, not phases for LCP, so we might want to do the same thing here (or object quickly on the LCP side of things :)

I'm cool with subparts so switched to that throughout.

[tunetheweb]

@rviscomi I've flattened the structure, and updated the comment in #574 (comment) to show that.

[rviscomi]

LGTM! I'll try it out in the next RC.