feat(GoogleMapsAPIWrapper): add panBy method

Author: jeffleeismyhero

src/core/services/google-maps-api-wrapper.ts

@@ -114,6 +114,10 @@ export class GoogleMapsAPIWrapper {
     return this._map.then((map) => map.panTo(latLng));
   }
 
+  panBy(x: number, y: number): Promise<void> {
+    return this._map.then((map) => map.panBy(x, y));
+  }
+
   fitBounds(latLng: mapTypes.LatLngBounds|mapTypes.LatLngBoundsLiteral): Promise<void> {
     return this._map.then((map) => map.fitBounds(latLng));
   }

src/core/services/google-maps-types.ts

@@ -4,6 +4,7 @@ export interface GoogleMap extends MVCObject {
   data?: Data;
   constructor(el: HTMLElement, opts?: MapOptions): void;
   panTo(latLng: LatLng|LatLngLiteral): void;
+  panBy(x: number, y: number): void;
   setZoom(zoom: number): void;
   getCenter(): LatLng;
   setCenter(latLng: LatLng|LatLngLiteral): void;