Merge remote-tracking branch 'upstream/virtual-scroll' into vs2

Author: mmalerba

src/demo-app/virtual-scroll/virtual-scroll-demo.ts

@@ -106,4 +106,11 @@ export class VirtualScrollDemo {
       return 0;
     }));
   }
+
+  sortBy(prop: 'name' | 'capital') {
+    this.statesObservable.next(this.states.map(s => ({...s})).sort((a, b) => {
+      const aProp = a[prop], bProp = b[prop];
+      return aProp < bProp ? -1 : (aProp > bProp ? 1 : 0);
+    }));
+  }
 }