Add TEST_MAPPING

We will run CellBroadcastServiceTests as part of presubmit for this
directory and postsubmit continuous testing.

Bug: 135956699
Test: none
Change-Id: I301c5c8be70f0f2c514f14138805a8c545dea074
Merged-In: I301c5c8be70f0f2c514f14138805a8c545dea074
1 file changed