Ensure ZoomView appears on top of other views in L

Since our normal image view now has an elevation on L, just calling
bringChildToFront() is not enough, elevation supersedes z order.
So we also ensure the ZoomView is at max elevation when we bring it
to front.

Bug: 17331586
Change-Id: I34b06949d063daa08d964003b28a245eb6133f95
2 files changed