Add expand icon for user switcher.

Adds the arrow to the left of the user name.
Animates the arrow in a sweet 180 degree rotation.

Bug: 65423882
Change-Id: I13a40dbd65c1335fdb579223d7c7cbd8623b3d6b
(cherry picked from commit f4d69c2b575940eca4620db5aec6d42b98b53071)