macOS: ask for a fresh capture while a resize waits for its paint

[wenkaifan0720]

Follow-up to #59. Checking the published c0576c5 prebuilt, device_frame failed one switch of 30. The view didn't freeze (frames kept coming), but one switch took over 4 s to repaint at the new size. The ad-hoc build did it too, just less often: #59's stall fallback ("kick") fired in 1 to 12 switches per run.

Cause

On macOS, CEF paints by capturing the root frame (CefVideoConsumerOSR). The capture size is the renderer's last activated frame size, set in OnRenderFrameMetadataChangedAfterActivation. A Chromium trace of a stall shows the sequence:

1. The new geometry goes out. The renderer is busy with the page's resize handler, and the display draws fallback frames.
2. The renderer's frame at the new size activates, and the capture size changes.
3. After one more capture, the display reports "No damage yet" on every begin frame, so the capturer has nothing to capture.

The capturer also drops refresh requests while it still sees the content as animating. ApplyGeometry's single Invalidate comes before all of this. No paint at the new size arrives until the 1 s kick swaps in a new surface id, which creates damage. Sometimes one kick wasn't enough, and it took 1 s + 2 s.

Fix

While a resize is in flight, CheckResizeStall (run every begin frame) calls Invalidate(PET_VIEW) every 100 ms. The kick stays as the fallback. Nothing changes when no resize is in flight.

Verification

• device_frame:
  • 5 runs: 0 kicks, 0 stuck. Before: 1 to 12 kicks per run; the published c0576c5 build failed 1 of 30.
  • Slowest switch: 1.3 s, down from 1.6 to 3.7 s. The page blocks for 600 ms on every resize.
  • One of the 5 runs was traced, which made stalls much more frequent before the fix (12 kicks); it had 0.
• hidden_at_create, surface_handoff, warm_host_paint, wedge_recovery, alert, multiview, profile_reopen: pass.
• New cef_host input hash: a91e6834…. The prebuilt needs republishing.

Windows is unchanged. windows-build fails the same software-compositing check on main (control run #60).

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