Comment 18 for bug 38939

Normally XAA gets a small portion of memory for offscreen allocation, but due to
rasterizer limits it only gets a smaller portion of memory and it just so
happens that the Xv allocator uses the same memory manager and suffers from the
same restrictions even though the hardware Xv setup doesn't have the limits.

So, we end up allowing the user to add extra memory resources to the allocator
specifically for Xv. We can define some conditions to allocate more Xv memory,
but it just hasn't been done and so it's left to the user to allocate it.