// We can't use Character.isSurrogate(c) because of GWT.

  public void testEncodedLength_validStrings() {
    assertEquals(0, Utf8.encodedLength(""));
    assertEquals(11, Utf8.encodedLength("Hello world"));
    assertEquals(8, Utf8.encodedLength("Résumé"));
    assertEquals(
        461,
        Utf8.encodedLength(
            "威廉·莎士比亞（William Shakespeare，"
                + "1564年4月26號—1616年4月23號[1]）係隻英國嗰演員、劇作家同詩人，"

   * time and space.
   *
   * @throws IllegalArgumentException if {@code sequence} contains ill-formed UTF-16 (unpaired
   *     surrogates)
   */
  public static int encodedLength(CharSequence sequence) {
    // Warning to maintainers: this implementation is highly optimized.
    int utf16Length = sequence.length();
    int utf8Length = utf16Length;
    int i = 0;