icu4c DateIntervalFormat objects are expensive enough that we need to cache them.
It takes ~1ms to create a DateIntervalFormat on a z620, and around 8ms on a
current mobile device (Nexus 4). Add a small cache of recently-used formatters,
using a big lock rather than per-thread caches since this typically only
happens on the UI thread anyway, and because all the other frameworks date/time
formatting is behind a single lock too.
Bug: 10696944
(cherry picked from commit fd1d5e92b2eaf785cb18aa295b7b846cfc5e29af)
Change-Id: Iefd573ff6f9851efda0ebe18418dba61fb151e65
3 files changed
