Measuring the notifications at wrap_content height now

The notifications are now measured at wrap_content such
that the layout still looks good even if the text
was ommited instead of arbitrarily making it bigger.
This also fixes some small rounding issues where the
expanded notification was just a pixel bigger than
the collapsed version.

Bug: 26185377
Change-Id: Ie3339ff75680ab512446605055304576e058f588