address comments

Author: mmalerba

src/cdk-experimental/scrolling/virtual-scroll-viewport.ts

@@ -150,9 +150,9 @@ export class CdkVirtualScrollViewport implements OnInit, OnDestroy {
     this._ngZone.runOutsideAngular(() => {
       this._forOf = forOf;
       this._forOf.dataStream.pipe(takeUntil(this._detachedSubject)).subscribe(data => {
-        const len = data.length;
-        if (len !== this._dataLength) {
-          this._dataLength = len;
+        const newLength = data.length;
+        if (newLength !== this._dataLength) {
+          this._dataLength = newLength;
           this._scrollStrategy.onDataLengthChanged();
         }
       });