Libunwindstack would remove duplicated items and update the `prev_map`
during reparsing `/proc/self/maps`. But we leave `prev_real_map`
pointing toward a MapInfo that will be deleted soon. It will cause a
dangling pointer issue.
Add new tests to cover this dangling pointer issue.
Bug: 155511785
Test: libunwindstack_test
Change-Id: I62e1b97bcb73f07e9349671f0b758f5ec9de16c0
(cherry picked from commit a7a194beb4)
Avoid accessing nullptr of already deleted entry.
Add new unit tests that pass with the fix and fail without.
Test: fixes unwinding in ART gcstress tests
Test: All unit tests pass.
Change-Id: Ideb00e2adc899904dd6aeb5dad3fb6fad150322d
Sim Sun