Fix split caused apps ANR

If mWindowDrawCountDown is set to non null when mReportNextDraw
is false, it won't get cleared in performingDraw.
If another draw occurs afterwards where mReportNextDraw is true,
but requestDrawWindow doesn't get called, an ANR will occur.
This is because performDraw will end up waiting forever since
mWindowDrawCountDown was previously set to non null,
but there will never be any calls reportDrawFinish to handle the
countDown.

We should only create latch and wait it when mReportNextDraw is
true.

Bug: 195262673
Test: Pass existing tests
Test: Drag and drop split divider quickly
Change-Id: I4ee81a41687c4f61a4828d4c61ba01abee795e89