Merge "Purge unused native memory before Zygote fork events" am: 0b242c8d

  android_fdsan_error_level fdsan_error_level = android_fdsan_get_error_level();

  // Purge unused native memory in an attempt to reduce the amount of false

  // sharing with the child process.  By reducing the size of the libc_malloc

  // region shared with the child process we reduce the number of pages that

  // transition to the private-dirty state when malloc adjusts the meta-data

  // on each of the pages it is managing after the fork.

  mallopt(M_PURGE, 0);

  pid_t pid = fork();

  if (pid == 0) {