code: function charsEndIndex(strSymbols, chrSymbols) {
      var index = strSymbols.length;
  
      while (index-- && baseIndexOf(chrSymbols, strSymbols[index], 0) > -1) {}
      return index;
    }
docs: Used by `_.trim` and `_.trimEnd` to get the index of the last string symbol
  that is not found in the character symbols.
  
  @private
  @param {Array} strSymbols The string symbols to inspect.
  @param {Array} chrSymbols The character symbols to find.
  @returns {number} Returns the index of the last unmatched string symbol.