[blink] Mark slow test as slow for streaming-preload

Duplicate a slow test for the streaming-preload virtual test.

Bug: 842995
Bug: 910846
Change-Id: Id3c5135d6585f4695ac33624ab563f3f867c685f
Reviewed-on: https://chromium-review.googlesource.com/c/1358500
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614684}
2 files changed