public Editor edit(String key) throws IOException {
    return edit(key, ANY_SEQUENCE_NUMBER);
  }
@Test public void cannotOperateOnEditAfterRevert() throws Exception {
    DiskLruCache.Editor editor = cache.edit("k1");
    editor.set(0, "A");
    editor.set(1, "B");
    editor.abort();
    assertInoperable(editor);
  }