[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}

third_party/blink/web_tests/SlowTests

@@ -361,6 +361,7 @@ crbug.com/826957 fast/peerconnection/RTCPeerConnection-manyCandidates.html [ Slo
 crbug.com/842995 external/wpt/html/semantics/scripting-1/the-script-element/execution-timing/078.html [ Slow ]
 crbug.com/626703 external/wpt/html/semantics/scripting-1/the-script-element/async_007.htm [ Slow ]
 crbug.com/626703 external/wpt/html/semantics/scripting-1/the-script-element/async_010.htm [ Slow ]
+crbug.com/842995 virtual/streaming-preload/external/wpt/html/semantics/scripting-1/the-script-element/execution-timing/078.html [ Slow ]
 crbug.com/626703 virtual/streaming-preload/external/wpt/html/semantics/scripting-1/the-script-element/async_007.htm [ Slow ]
 crbug.com/626703 virtual/streaming-preload/external/wpt/html/semantics/scripting-1/the-script-element/async_010.htm [ Slow ]
 

third_party/blink/web_tests/TestExpectations

@@ -5718,9 +5718,6 @@ crbug.com/908347 [ Mac ] media/autoplay/webaudio-audio-context-resume.html [ Fai
 crbug.com/910139 custom-elements/form-submission-file.html [ Crash Pass ]
 crbug.com/905772 [ Linux ] inspector-protocol/memory/sampling-native-profile-blink-gc.js [ Failure Pass ]
 
-#Sheriff 2018-12-03
-crbug.com/910846 [ Win ] virtual/streaming-preload/external/wpt/html/semantics/scripting-1/the-script-element/execution-timing/078.html [ Failure Pass Timeout ]
-
 #Sheriff 2018-12-04
 crbug.com/911515 [ Mac ] transforms/shadows.html [ Pass Failure ]
 crbug.com/911634 [ Linux ] fast/events/touch/gesture/touch-gesture-scroll-input-field.html [ Pass Failure ]