commit 0165cb697466ba0843b993416e00d4f768c00d45 changed
mutter to release committed shm buffers as soon as they were
uploaded to the GPU.
It also inadvertently changed mutter to prematurely
release EGL buffers (which never get copied, but get used
directly).
This commit corrects that mistake.
https://bugzilla.gnome.org/show_bug.cgi?id=761312