If false, the start drawable will not fade out while the end drawable fades in.
preferExactIntrinsicSize
If true, this drawable's intrinsic width/height will only be -1 if startandend return -1 for that dimension. If false, the intrinsic width/height will be -1 if startorend return -1 for that dimension. This is useful for views that require an exact intrinsic size to scale the drawable.