Disable http/tests/devtools/elements/styles-4/stylesheet-source-url-comment.js

Disable the test due to Timeout

Bug: 938883
Change-Id: Id2b1f3bed6f8044bd8426dc42ac021ac2ec440ab
Bug: 938883
Tbr: petewil@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1506117Reviewed-by: Owen Min <zmin@chromium.org>
Commit-Queue: Owen Min <zmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#638224}

third_party/blink/web_tests/TestExpectations

@@ -5154,7 +5154,7 @@ crbug.com/828858 external/wpt/inert/inert-node-is-uneditable.tentative.html [ Fa
 # Sheriff 2018-06-07
 crbug.com/850395 virtual/gpu/fast/canvas/canvas-filter-stroke-paint-pattern.html [ Pass Failure ]
 crbug.com/850358 http/tests/devtools/editor/text-editor-enter-behaviour.js [ Pass Failure Timeout ]
-crbug.com/849978 http/tests/devtools/elements/styles-4/stylesheet-source-url-comment.js [ Pass Failure ]
+crbug.com/849978 http/tests/devtools/elements/styles-4/stylesheet-source-url-comment.js [ Pass Failure Timeout ]
 
 # Sheriff 2018-06-08
 crbug.com/850170 virtual/reporting-api/external/wpt/content-security-policy/reporting-api/reporting-api-doesnt-send-reports-without-violation.https.sub.html [ Pass Crash Timeout ]