Notification for changed subtree in accessibility mode not fired properly.

We fire notifications that the a view subtree changed for accessibility.
In some cases the notifications were fired if accessibility is not
enabled. This is now fixed. Also the runnable for making the recurring
subtree change was not dequeued if it was pending but we received a
request which we decided to run immediately.

bug:9337912

Change-Id: I27401b3d11f81c653e8761a704ee530263b08c3a