Fixed an issue where the contentHeight was calculated wrongly

We adjusted the algorithm to include gaps before certain views
but never updated the contentHeight of the layout.
Those minor differences could lead to issues where a user couldn't
see the clear all in certain cases or where the expansion would
jump.

Fixes: 153321587
Test: add notification with 2 min priority notifications, expand, observe no flickering at the end
Change-Id: Iebf6493136b8c7784e41ab27891ffd225aa0fd54