GC events are reported with wrong units on logging page

[DanTup]

See dart-lang/sdk#54692 (comment) - the GC events being shown are reported as ms but are apparently microseconds, not milliseconds.

[kenzieschmoll]

Here is an example GC event we get in the logging page:

  "reason": "idle",
  "new": {
    "type": "HeapSpace",
    "name": "new",
    "vmName": "Scavenger",
    "collections": 257,
    "avgCollectionPeriodMillis": 334489.74241634243,
    "used": 3104,
    "capacity": 524288,
    "external": 224,
    "time": 0.170491
  },
  "old": {
    "type": "HeapSpace",
    "name": "old",
    "vmName": "PageSpace",
    "collections": 30,
    "used": 86273376,
    "capacity": 92065792,
    "external": 21776,
    "time": 0.12025,
    "avgCollectionPeriodMillis": 2865462.1269
  },
  "isolate": {
    "type": "@Isolate",
    "id": "isolates/8828232814957387",
    "name": "main",
    "number": "8828232814957387",
    "isSystemIsolate": false,
    "isolateGroupId": "isolateGroups/3684315914930295"
  }
}

@rmacnak-google in this comment you mentioned that the units are incorrect. What units is the "time" field for the new and old entries in the map above?

We calculate the time as follows:

final time = ((newSpace.time! + oldSpace.time!) * 1000).round();

where newSpace.time and oldSpace.time are the raw double values from the "old" and "new" json entires.