remeasure when overlay views change size

The initial measure() (for sending to WebView) is done too soon,
so after a height change, ensure that the container re-measures.
The container will only measure newly bound views, or views with
newly changed heights, so most scrolling continues to not
trigger measure().

It would be more correct to mark the overlay *view* itself
valid or invalid, not the item, but apps don't have access to
the measurement flags on View.

Also do lots of cleanup in the area of measure/layout of the
Container. Prevent children of the container from requesting
layout because they don't push on each other in the normal way.
(a followup onGeometryChange is needed to re-position properly)
But a layout triggered from elsewhere should re-measure and
re-position the container's overlays.

Bug: 6297423

Change-Id: Id9196322774e732417e926ac87ce2ec524bf425e
4 files changed