Signature for Window.onReportTimings.
The callback takes a list of FrameTiming because it may not be immediately triggered after each frame. Instead, Flutter tries to batch frames together and send all their timings at once to decrease the overhead (as this is available in the release mode). The list is sorted in ascending order of time (earliest frame first). The timing of any frame will be sent within about 1 second (100ms if in the profile/debug mode) even if there are no later frames to batch.
typedef TimingsCallback = void Function(List<FrameTiming> timings);