Mark external/wpt/resource-timing/nested-context-navigations.html as flaky

TBR=npm@chromium.org

Bug: 957181
Change-Id: I94d905ce74365b5f5864797941019424aa0a6c82
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1585116Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Dmitry Gozman <dgozman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654596}

third_party/blink/web_tests/TestExpectations

@@ -2511,6 +2511,8 @@ crbug.com/613672 [ Mac ] virtual/user-activation-v2/fast/events/touch/gesture/to
 crbug.com/802067 [ Mac ] external/wpt/pointerlock/movementX_Y_basic.html [ Failure ]
 crbug.com/802067 [ Mac ] external/wpt/pointerevents/pointerlock/pointerevent_movementxy-manual.html [ Failure ]
 
+crbug.com/957181 external/wpt/resource-timing/nested-context-navigations.html [ Pass Failure ]
+
 # Since there is no compositor thread when running tests then there is no main thread event queue. Hence the
 # logic for this test will be skipped when running Layout tests.
 crbug.com/770028 external/wpt/pointerevents/extension/pointerevent_pointerrawmove-manual.html [ Skip ]