fix(router): lazy loading keeps refetching modules (#10707)

modules/@angular/router/test/apply_redirects.spec.ts

@@ -266,6 +266,32 @@ describe('applyRedirects', () => {
         expect((<any>config[1])._loadedConfig).toBe(loadedConfig);
       });
     });
+
+    it('should load the configuration only once', () => {
+      const loadedConfig = new LoadedRouterConfig(
+          [{path: '', component: ComponentB}], <any>'stubInjector', <any>'stubFactoryResolver');
+
+      let called = false;
+      const loader = {
+        load: (injector: any, p: any) => {
+          if (called) throw new Error('Should not be called twice');
+          called = true;
+          return of (loadedConfig);
+        }
+      };
+
+      const config = [{path: 'a', loadChildren: 'children'}];
+
+      applyRedirects(<any>'providedInjector', <any>loader, tree('a?k1'), config).subscribe(r => {});
+
+      applyRedirects(<any>'providedInjector', <any>loader, tree('a?k2'), config)
+          .subscribe(
+              r => {
+                compareTrees(r, tree('a'));
+                expect((<any>config[0])._loadedConfig).toBe(loadedConfig);
+              },
+              (e) => { throw 'Should not reach'; });
+    });
   });
 
   describe('empty paths', () => {