int computeMissedFrameRasterizerBudgetCount([Duration frameBuildBudget = kBuildBudget ])

The number of frames that missed the kBuildBudget on the GPU and therefore are in the danger of missing frames.

Source 

int computeMissedFrameRasterizerBudgetCount([Duration frameBuildBudget = kBuildBudget]) => _extractGpuRasterizerDrawEvents()
    .where((TimedEvent event) => event.duration > kBuildBudget)
    .length;