tombstoned: add tests for b/36685795.

Add some tests for edge cases which may have triggered b/36685795.

Bug: http://b/36685795
Test: debuggerd_test
Change-Id: I20670684c8dae422af157be21e44ba5d6d3214d3
(cherry picked from commit 352a84574dd0f3be0c30d15c0c577c226ec28c2f)
2 files changed