[Ongoing Call Chip] UI tweaks: Don't have the chip width change each

second, and hide the time if it's too large for the space available.

Demo: b/185897063#comment2

Test: atest (including new OngoingCallChronometerTest) and manual
Bug: 183229367
Fixes: 185897184, 185897063
Change-Id: I7fb129734cd1dc29f45e41e6e1775d44f1680d10