code: function Struct(properties) {
                  this.fields = {};
                  if (properties)
                      for (var keys = Object.keys(properties), i = 0; i < keys.length; ++i)
                          if (properties[keys[i]] != null)
                              this[keys[i]] = properties[keys[i]];
              }
docs: Properties of a Struct.
  @memberof google.protobuf
  @interface IStruct
  @property {Object.<string,google.protobuf.IValue>|null} [fields] Struct fields
   
  Constructs a new Struct.
  @memberof google.protobuf
  @classdesc Represents a Struct.
  @implements IStruct
  @constructor
  @param {google.protobuf.IStruct=} [properties] Properties to set