code: function getMessageFromRegistry(messageType, type) {
    var packageName = getPackageNameFromMessageType(messageType);
    var messageName = getMessageNameFromMessageType(messageType);
    var packageSection = registry[packageName];
    if (!packageSection) {
      return undefined;
    }
    var section = registry[packageName][type]; // msg or srv sub-object
    if (!section) {
      return undefined;
    }
    return section[messageName];
  }
docs: /*
  registry looks like:
  { 'packagename':
  {
  msg: {
  'String': classdef,
  'Pose': classdef,
  ...
  },
  srv: { Request:
  {
  'SetBool': classdef,
  ...
  },
  Response:
  {
  'SetBool': classdef,
  ...
  }
  }
  },
  'packagename2': {..}
  };
   
  @param messageType is the ROS message or service type, e.g.
  'std_msgs/String'
  @param type is from the set
  ["msg", "srv"]