[libFuzzer] reimplement experimental_len_control=1: bump the temporary max_len every time we failed to find new coverage during the last 1000 runs and 1 second. Also fix FileToVector to not load unfinished files 

git-svn-id: svn://svn.chromium.org/llvm-project/llvm/trunk/lib/Fuzzer@308811 0b72dbe1-c17f-4bc7-b9db-2b4152be0356
4 files changed