Fix a few warnings (signed/unsigned comparison in gtest, and missing field initializers) am: 6841f6e058 am: 6b63e40153 am: 1cb5745a89

Original change: https://android-review.googlesource.com/c/platform/external/gwp_asan/+/1860473

Change-Id: If4fe32be627206b37f1b0b56227bd21f3cfc7922