crosperf: add results_cache_unittest

BUG=None
TEST=this unittest passes.

Change-Id: I65fee19efd30b1602a6ad49b84abe7366a6e605c
Reviewed-on: https://gerrit-int.chromium.org/38429
Reviewed-by: Yunlian Jiang <yunlian@google.com>
Tested-by: Yunlian Jiang <yunlian@google.com>
Commit-Queue: Yunlian Jiang <yunlian@google.com>
1 file changed