Add java.time.chrono.Era tests.

Cover Era.getLong method with tests.

Bug: 182165762
Test: atest libcore.java.time.chrono.EraTest
Change-Id: I0dbe7193480c5ca12b26ad95529127e1e8e4a1fb
Merged-In: I0dbe7193480c5ca12b26ad95529127e1e8e4a1fb
(cherry picked from commit 8be600c784cc208b23d45ca88dda65a430fa065d)
1 file changed