docs: function parseResponseHeaders(headerStr) {
      var headers = {};
      if (!headerStr) {
          return headers;
      }
      var headerPairs = headerStr.split('\u000d\u000a');
      for (var i = 0; i < headerPairs.length; i++) {
          var headerPair = headerPairs[i];
          // Can't use split() here because it does the wrong thing
          // if the header value has the string ": " in it.
          var index = headerPair.indexOf('\u003a\u0020');
          if (index > 0) {
              var key = headerPair.substring(0, index);
              var val = headerPair.substring(index + 2);
              headers[key] = val;
          }
      }
      return headers;
  }