Make 2040-huge-native-alloc more robust

Most importantly, call gc() before we start, so we start with a clean
slate.

Allocate a bit more to make sure we're over the threshold for
triggering blocking.

Get a third reference time. Try twice to trigger a blocking GC.

Bug: 190148586
Test: run-test --host 2040-huge-native-alloc
Change-Id: If7f8aa8baec715c6f295384ce70b0b349ea2c71d
1 file changed