Chun-Min Chang authored Jul 21, 2020 and Matthew Finkel committed Mar 17, 2021

The `gCombinedSizes` need to be enlarged once the inner buffer within
`MemoryBlockCache` grows. Otherwise, when the `MemoryBlockCache` is
released, subtracting the buffer-size of the `MemoryBlockCache` from
`gCombinedSizes` lead to a underflow.

Differential Revision: https://phabricator.services.mozilla.com/D84273