Mark xhr/responsexml-document-properties.htm as flaky

The web platform test xhr/responsexml-document-properties.htm is flaky.
Mark it as such in TestExpectations.

BUG=1144537

Change-Id: Ic7de8bb61f7646127c4094a9f88c066895189b6a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2515419
Commit-Queue: Adam Rice <ricea@chromium.org>
Commit-Queue: Nate Chapin <japhet@chromium.org>
Auto-Submit: Adam Rice <ricea@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823371}

third_party/blink/web_tests/TestExpectations

@@ -1695,7 +1695,6 @@ crbug.com/1049641 [ Debug ] http/tests/devtools/sources/debugger-breakpoints/set
 crbug.com/1049641 http/tests/devtools/sources/debugger/debugger-disable-enable.js [ Pass Timeout ]
 
 # Sheriff 2019-08-19
-crbug.com/626703 [ Win7 ] external/wpt/xhr/responsexml-document-properties.htm [ Failure ]
 crbug.com/626703 [ Win7 ] external/wpt/html/dom/documents/resource-metadata-management/document-lastModified-01.html [ Failure ]
 
 # These are added to W3CImportExpectations as Skip, remove when next import is done.
@@ -6228,3 +6227,5 @@ crbug.com/1144677 external/wpt/css/css-backgrounds/border-radius-clip-001.html [
 crbug.com/1144677 external/wpt/css/css-backgrounds/border-radius-clip-002.htm [ Pass Failure ]
 crbug.com/1144677 external/wpt/infrastructure/reftest/reftest.www.sub.html [ Failure ]
 crbug.com/1144677 external/wpt/paint-timing/fcp-only/fcp-ensure-update-the-rendering-step.html [ Pass Failure ]
+
+crbug.com/1144537 external/wpt/xhr/responsexml-document-properties.htm [ Pass Failure ]