ReferenceError: google is not defined

This error most likely occurs since the moment when allowedBounds is getting initialized, Google Maps API is not yet loaded and therefore Google Maps objects like google.maps.LatLngBounds are not yet available. agm-map ships with loader which loads Google Maps library asynchronously.

In order to ensure Google Maps API is loaded, MapsAPILoader service could be utilized as demonstrated below:

export class AppComponent  {
  bounds = null;

  constructor(private mapsAPILoader: MapsAPILoader) {
    this.mapsAPILoader.load().then(() => {
      this.bounds = new google.maps.LatLngBounds(
        new google.maps.LatLng(51.130739, -0.868052), // SW
        new google.maps.LatLng(51.891257, 0.559417) // NE
      );
      console.log(this.bounds);
    });
  }

}

Here is a demo which demonstrates how to fit a map for a given bounds