Restore opaque alpha value when AlphaAnimation finishes

Alpha values were being set correctly on native Display Lists during an
AlphaAnimation, but not when the animation finished. Only non-1 values
were being propagated to the Display List properties.

The fix is to track when we've set a non-1 alpha value from an AlphaAnimation
and to notice that flag when the value is 1 (because the animation ended), so that
we propagate that value correctly. Using the flag avoids sending a value of 1
(by far the most common case) unless we really need to restore it after animating
it with non-1 values.

Issue #6600592 Sometimes album art blends with list asset on queue

Change-Id: I51047d756a4ac42a2d907a4d77963cc23dfb1db3