It is possible for the content that layers represent to change size, causing
tiles to be reused where they shouldn't. Make sure that tiles that are outside
of content bounds are not drawn, and that they get evicted when harvesting
tiles.
Rather than discarding uploaded tiles once they fall outside of the valid
region, shuffle them off into a separate tile-store with all the metadata they
need to render them, and render them in the areas that our current valid
region doesn't cover in TiledThebesLayerOGL::RenderLayer.
Rather than discarding uploaded tiles once they fall outside of the valid
region, shuffle them off into a separate tile-store with all the metadata they
need to render them, and render them in the areas that our current valid
region doesn't cover in TiledThebesLayerOGL::RenderLayer.
