Code review comment for lp://qastaging/~alan-griffiths/mir/fix-1535894

Then again, if we don't intend to try and animate both screens at once then that's probably OK...

I'll stop short of approving though, because there's an additional problem with this branch that will break free-form rendering like Compiz or mir_proving_server -- Some pixels are painted outside of the surface itself (like shadows or other effects like minimizing animation). As such, your view area test will be wrong, and will fail to update the secondary screen when it needs updating.

Worse again, this change will fail completely under full screen transformations like desktop zoom. And again will fail to refresh displays correctly, appearing to freeze instead.

I actually disapprove, but will abstain because can see it will help pocket desktop as it stands right now.