Don't let two close frames to interrupt intermittency

Fixes: 336840867

There is a common case where two frames follow quickly during
intermittent updates. This CL requires that at least three
frames take less than 100ms before intermittency is not considered.

Also, some same-frame movement results in 0 overall motion.
For example, a setFrame() call that moves content will follow-on
with an offsetTopAndBottom() that moves it back. Now, the
previous frame's position is tracked and compared instead
of only flagging the motion.

Test: new test, existing tests
Change-Id: Ia2c9dbc5485b0af34b4f4aa5f3a1dda4cb8552f7