fd_utils: Fix broken usage of iterators.

    //

    // (a) they continue to be open.

    // (b) they refer to the same file.

    std::unordered_map<int, FileDescriptorInfo*>::iterator it;

    for (it = open_fd_map_.begin(); it != open_fd_map_.end(); ++it) {

    std::unordered_map<int, FileDescriptorInfo*>::iterator it = open_fd_map_.begin();

    while (it != open_fd_map_.end()) {

      std::set<int>::const_iterator element = open_fds.find(it->first);

      if (element == open_fds.end()) {

        // The entry from the file descriptor table is no longer in the list

        // TODO(narayan): This will be an error in a future android release.

        // error = true;

        // ALOGW("Zygote closed file descriptor %d.", it->first);

        open_fd_map_.erase(it);

        it = open_fd_map_.erase(it);

      } else {

        // The entry from the file descriptor table is still open. Restat

        // it and check whether it refers to the same file.

        open_fds.erase(element);

        const bool same_file = it->second->Restat();

        if (!same_file) {

          // The file descriptor refers to a different description. We must

            // We flag an error and remove it from the list of files we're

            // tracking.

            error = true;

            open_fd_map_.erase(it);

            it = open_fd_map_.erase(it);

          } else {

            // Successfully restatted the file, move on to the next open FD.

            ++it;

          }

        } else {

          // It's the same file. Nothing to do here.

          // It's the same file. Nothing to do here. Move on to the next open

          // FD.

          ++it;

        }

        // Finally, remove the FD from the set of open_fds. We do this last because

        // |element| will not remain valid after a call to erase.

        open_fds.erase(element);

      }

    }