nghand property.
  style.removeProperty("position");
  assert_no_record("removing non-existing longhand property");
  style.setProperty("position", "");
  assert_no_record("setting empty string to non-existing longhand property");
  // Shorthand property.
  style.removeProperty("margin");
  assert_no_record("removing non-existing shorthand property");
  style.setProperty("margin", "");
  assert_no_record("setting empty string to non-existing shorthand property");
  // Check that the value really isn't chang