Make Animation.cancel() actually work

Cancel() has apparently never worked. Calling cancel() results
in the startTime being set to Long.MIN_VALUE. In theory, this means that
on the next animation frame (getTransformation()), the elapsed time
(currentTime - startTime) should result in a large positive number, which
is way more than needed to prove that the elapsed fraction is >1 and
therefore that the animation has ended. But in practice, anything subtracting
MIN_VALUE will result in a large negative number due to Long wraparound, so the
end check fails and the animation continues. Forever.

Moreover, event fixing the cancel issue results in a repeating animation
continuing to repeat, because the logic was never there to determine whether
a repeating animation was canceled.

This fix addresses both issues, but in a minimal way. The risk in fixing this
for real is changing the behavior of cancel in a way that existing apps would not
expect. For example, it's weird that cancel causes one more frame to run. And even weirder
that it does so with a negative elapsed duration (resulting in an animation fraction of 0).
But I wouldn't want to change that behavior for fear that I'd break apps who rely on
that weird behavior.

Instead, there's a simple check for for the "expired" check and the "repeat?" check that
sees whether the startTime has the magic value of MIN_VALUE, which should only happen
when an animation has been canceled. If this is the case, it ensures that the animation ends.
For real.

Issue #24984018 canceled animation runs forever

Change-Id: Ia137eb04bd7df3976a4d9cef86fd39a78dc56f39