* Added return value to a onNotification callback.

The LayoutChangedNotification callback was missing a return value.
This commit changes it to return true and stop notification from
bubbling up the tree.

* Changed _RenderInkFeatures to use fresh clip box.

Since it wasn't using the most current value of the RenderBox's
size, _RenderInkFeatures was rendering splashes incorrectly when
the underlying Material size was animating. This commit changes
the clip reference to use the size of the Renderbox instead of
the size method in order to get the newest value.