Fix issue with LayoutTransition on non-visible windows.

There's a problem with how LayoutTransition cleans up after itself
when the target view is in a Window that is not on the screen.
The quick fix is to always start (and therefore properly end and clear)
transitions, regardless of whether the window is in the tree.

Change-Id: I23f4f4f04176f3943e5c6e1d78acba0190a96930