CreateDefaultDisplayReporter() transfers ownership of the returned
reporter to the caller, but cached that owning pointer in a
function-local static. After the first RunSpecifiedBenchmarks() call
destroyed the reporter, a subsequent call returned the same, now
dangling pointer, causing a heap-use-after-free in
BenchmarkReporter::GetOutputStream().
Return std::unique_ptr<BenchmarkReporter> so the ownership transfer is
expressed in the type, and drop the static so every call returns a
fresh reporter.
Tejas Anil Nagmote
bb682b4d7f