@Override
  void copyContentTo(File file) throws IOException {
    RegularFile copy = (RegularFile) file;
    disk.allocate(copy, blockCount);

    for (int i = 0; i < blockCount; i++) {
      byte[] block = blocks[i];
      byte[] copyBlock = copy.blocks[i];
      System.arraycopy(block, 0, copyBlock, 0, block.length);
    }
  }
Gets the current size of this file in bytes. Does not do locking, so should only be called when
holding a lock.
jimfs/src/main/java/com/google/common/jimfs/RegularFile.java