Reducing layer tree pipeline depth to 2 (from 3) regressed performance

[Hixie]

The flutter_gallery_ios__transition_perf average_frame_rasterizer_time_millis benchmark regressed substantially when we landed flutter/engine#3909.

[Hixie]

The patch is simple enough that we can investigate its implications at our leisure.

@j9brown suggested:

I recommend collecting traces from the device in each mode. The pattern
should become more obvious.

Depending on how your logic is constructed you might be ending up in a
double buffered mode instead of triple buffered and that can make all the
difference. Noting of course that there's a trade-off between latency and
throughput.

[cbracken]

/cc @chinmaygarde do you think it's worth closing this given that reducing the pipeline depth was done with a goal of reducing jank? Given the age of this, tempted to close as obsolete unless you think there's a good reason to revert.

[github-actions]

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