Code review comment for lp://staging/~nick-dedekind/qtmir/multiwindow.textures

> In MirSurface::dropPendingBuffer() looks like you're replacing it with its old
> implementation. Is that intentional? If not, please update the current
> implementation to work with that new multi-texture scenario.

It was intentional.
Your reason for changing the code was "Make frame dropper work even when there's no texture around".
In this impl for the frame dropper we iterate over the textures which we have already generated and update the texture. We wouldn't have any renderables for something we hadn't requested (and therefore have a texture).