Not all pending display list epochs are painted immediately or at all.
Soemtimes WebRender is one or more display lists behind the latest and
sometimes an epoch isn't painted at all if a new display list arrives
before the old one is painted. These situations aren't errors, but they
might indicate performance issues.
Instead of forever printing warnings when this happens, properly clean
up pending paint metrics after compositing. If earlier pending paint
metrics for a pipeline exist, remove them. If a pipeline is no longer
known by the compositor, remove its pending paint metrics.
This change fixes situations where warnings flood the output and a small
memory leak.
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
Co-authored-by: Mukilan Thiyagarajan <mukilan@igalia.com>
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