Disable more http/tests/devtools/sxg/ tests

This CL disables the http/tests/devtools/sxg/sxg-prefetch-fail.js and
http/tests/devtools/sxg/sxg-prefetch.js for virtual/sxg-with-network-service as
well.

TBR=horo@chromium.org

Bug: 851363,950083
Change-Id: Ifc5d93e7637179cb3774dd9192f8829f5211198b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1556791Reviewed-by: Dominic Battré <battre@chromium.org>
Commit-Queue: Dominic Battré <battre@chromium.org>
Cr-Commit-Position: refs/heads/master@{#648682}

third_party/blink/web_tests/TestExpectations

@@ -5114,8 +5114,10 @@ crbug.com/818650 [ Linux ] fast/speech/scripted/speechrecognition-restart-onend.
 # Prefetching Signed Exchange DevTools tests are flaky.
 crbug.com/851363 http/tests/devtools/sxg/sxg-prefetch-fail.js [ Pass Failure ]
 crbug.com/851363 virtual/nobinary-for-devtools/http/tests/devtools/sxg/sxg-prefetch-fail.js [ Pass Failure ]
+crbug.com/851363 virtual/sxg-with-network-service/http/tests/devtools/sxg/sxg-prefetch-fail.js [ Pass Failure ]
 crbug.com/851363 http/tests/devtools/sxg/sxg-prefetch.js [ Pass Failure ]
 crbug.com/851363 virtual/nobinary-for-devtools/http/tests/devtools/sxg/sxg-prefetch.js [ Pass Failure ]
+crbug.com/851363 virtual/sxg-with-network-service/http/tests/devtools/sxg/sxg-prefetch.js [ Pass Failure ]
 
 # Sheriff 2018-03-22
 crbug.com/824775 [ Win ] media/controls/video-controls-with-cast-rendering.html [ Pass Failure ]