function inherit(parent, extra) {
  return extend(new (extend(function() {}, {prototype:parent}))(), extra);
}
@ngdoc function
@name angular.extend
@module ng
@kind function

@description
Extends the destination object `dst` by copying all of the properties from the `src` object(s)
to `dst`. You can specify multiple `src` objects.

@param {Object} dst Destination object.
@param {...Object} src Source object(s).
@returns {Object} Reference to `dst`.