How much revenue does Metamask make in swap fees?

According to Metamask FAQ they charge between 0.3% – 0.875% per swap. Does anyone know if that's a fee of the gross transaction volume or a percentage of the gas fee?

For example if I'm swapping $10,000 in ETH<>USDC, and the gas+fee to swap on Uniswap is $180, does Metamask add $30 for themselves (0.3% * 10,000) or $0.54 (0.3% * $180)