Add idle frame support to Performance timeline - #57952
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Summary:
Implement Idle frame spans in Chrome DevTools, by emitting synthetic `NeedsBeginFrameChanged` + `BeginFrame` events.
**Definition**
An idle frame is emitted whenever the gap between two consecutive frames exceeds one vsync interval, derived from the display's refresh rate (`CADisplayLink.duration` on iOS, `Display.refreshRate` on Android, falling back to 60 Hz).
```
frame N gap > 1 vsync frame N+1
+------------+ +--------------------------------+ +------------+
| BeginFrame | | NeedsBeginFrameChanged | | BeginFrame |
| DrawFrame | | BeginFrame (no DrawFrame) | | DrawFrame |
+------------+ +--------------------------------+ +------------+
rendered as an "Idle frame"
```
**Implementation notes**
- Drop frames that begin before the recording start — Android `FrameMetrics` can deliver frames from app startup, and the first iOS `CADisplayLink` callback reports the previous vsync.
- Sort frames by begin timestamp before serializing, since async screenshot encoding can deliver them out of order and break gap detection.
- iOS: skip the frame event when the screenshot is unchanged, letting the gap render as an idle frame.
Changelog: [Internal]
Differential Revision: D97502569
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Summary:
Implement Idle frame spans in React Native DevTools, by emitting synthetic
NeedsBeginFrameChanged+BeginFrameevents.Definition
An idle frame is emitted whenever the gap between two consecutive frames exceeds one vsync interval, derived from the display's refresh rate (
CADisplayLink.durationon iOS,Display.refreshRateon Android, falling back to 60 Hz).Implementation notes
FrameMetricscan deliver frames from app startup, and the first iOSCADisplayLinkcallback reports the previous vsync.Changelog: [Internal]
Differential Revision: D97502569