Temporarily mark an upcoming test from WPT as failing.

test-results.appspot.com is returning an HTTP 500 error code when
`webkit-patch rebaseline-cl` tries to fetch the -actual.txt files to
rebaseline the test, and this is blocking WPT imports.

TBR=robertma,lukebjerring

Bug: 813762
Change-Id: Idd1ae8263d3a16f796cca3080913478f39b293d1
No-Try: True
Reviewed-on: https://chromium-review.googlesource.com/925705Reviewed-by: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Commit-Queue: Raphael Kubo da Costa <raphael.kubo.da.costa@intel.com>
Cr-Commit-Position: refs/heads/master@{#537757}

third_party/WebKit/LayoutTests/TestExpectations

@@ -3314,3 +3314,6 @@ crbug.com/812941 [ Win7 ] external/wpt/css/css-multicol/multicol-span-all-margin
 crbug.com/812941 [ Win7 ] external/wpt/css/css-multicol/multicol-table-cell-vertical-align-001.xht [ Failure Pass ]
 
 crbug.com/813704 [ Win7 Mac ] http/tests/images/png-partial-load-as-document.html [ Failure Pass ]
+
+# TODO(rakuco): Remove after the corresponding bug is solved on the infra side.
+crbug.com/813762 external/wpt/html/browsers/browsing-the-web/navigating-across-documents/javascript-url-abort/javascript-url-abort-return-value-string.tentative.html [ Failure ]