Disable flaky idl harness test on MSAN bot

Bug: 856601
Change-Id: Iebfdce6071ece01fb82d480139b2c92837467628
TBR: robertma@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1789962Reviewed-by: Ian Clelland <iclelland@chromium.org>
Commit-Queue: Ian Clelland <iclelland@chromium.org>
Cr-Commit-Position: refs/heads/master@{#694277}

third_party/blink/web_tests/MSANExpectations

@@ -347,7 +347,7 @@ crbug.com/856601 [ Linux ] external/wpt/BackgroundSync/idlharness.https.any.work
 crbug.com/856601 [ Linux ] external/wpt/fetch/api/idlharness.any.serviceworker.html [ Pass Timeout ]
 crbug.com/856601 [ Linux ] external/wpt/BackgroundSync/idlharness.https.any.html [ Pass Timeout ]
 
-# Sheriff 2009-09-05
+# Sheriff 2019-09-05
 crbug.com/856601 [ Linux ] external/wpt/fetch/api/idlharness.any.html [ Pass Timeout ]
 crbug.com/856601 [ Linux ] external/wpt/fetch/api/idlharness.any.sharedworker.html [ Pass Timeout ]
 crbug.com/856601 [ Linux ] external/wpt/generic-sensor/idlharness.https.window.html [ Pass Timeout ]
@@ -359,4 +359,7 @@ crbug.com/856601 [ Linux ] virtual/blink-cors/external/wpt/fetch/cors-rfc1918/id
 crbug.com/856601 [ Linux ] virtual/omt-worker-fetch/external/wpt/fetch/cors-rfc1918/idlharness.tentative.any.worker.html [ Pass Timeout ]
 crbug.com/856601 [ Linux ] virtual/omt-worker-fetch/external/wpt/resource-timing/idlharness.any.worker.html [ Pass Timeout ]
 
+# Sheriff 2019-09-06
+crbug.com/856601 [ Linux ] external/wpt/idle-detection/idlharness.https.any.html [ Pass Timeout ]
+
 # Note to sheriffs: Timeouts about "idlharness" or "interfaces" are usually crbug.com/856601.