Mark virtual/new-remote-playback-pipeline/media/controls/modern/scrubbing.html slow

Other versions of media/controls/modern/scrubbing.html are marked slow,
but not virtual/new-remote-playback-pipeline/, causing this to flakily
time out.

Bug: 793771, 850116
Change-Id: I3a45716ebd797f781573b2d5d86dfa58b213b271
Reviewed-on: https://chromium-review.googlesource.com/1089384Reviewed-by: Tommy Steimel <steimel@chromium.org>
Commit-Queue: Kevin McNee <mcnee@chromium.org>
Cr-Commit-Position: refs/heads/master@{#565012}

third_party/WebKit/LayoutTests/SlowTests

@@ -441,6 +441,7 @@ crbug.com/779956 [ Linux ] external/wpt/offscreen-canvas/drawing-images-to-the-c
 crbug.com/779956 [ Linux ] external/wpt/offscreen-canvas/drawing-images-to-the-canvas/2d.drawImage.zerosource.worker.html [ Slow ]
 
 crbug.com/793771 media/controls/modern/scrubbing.html [ Slow ]
+crbug.com/793771 virtual/new-remote-playback-pipeline/media/controls/modern/scrubbing.html [ Slow ]
 crbug.com/793771 virtual/video-surface-layer/media/controls/modern/scrubbing.html [ Slow ]
 
 # These tests need to do many iterations and so can't be fast.