Mark some Web Authentication API tests as flaky.

TBR=pkasting@chromium.org
NOTRY=true (disabling tests)

Bug: 875444
Change-Id: I25183c656dab7f8ef061d2261dbfe517369f68ba
Reviewed-on: https://chromium-review.googlesource.com/1179257Reviewed-by: apacible <apacible@chromium.org>
Commit-Queue: apacible <apacible@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584191}

third_party/WebKit/LayoutTests/TestExpectations

@@ -4550,19 +4550,21 @@ crbug.com/785955 http/tests/credentialmanager/tools/virtual-authenticator-enviro
 # These Web Authentication API would require either real hardware, or
 # virtual simulation thereof (work in progress, see: https://crbug.com/785955).
 crbug.com/826936 external/wpt/webauthn/createcredential-badargs-authnrselection.https.html [ Pass Timeout ]
-crbug.com/826936 external/wpt/webauthn/createcredential-badargs-challenge.https.html [ Pass Timeout ]
 crbug.com/826936 external/wpt/webauthn/createcredential-badargs-rp.https.html [ Pass Timeout ]
 crbug.com/826936 external/wpt/webauthn/createcredential-badargs-user.https.html [ Pass Timeout ]
 crbug.com/826936 external/wpt/webauthn/createcredential-excludecredentials.https.html  [ Pass Timeout ]
 crbug.com/826936 external/wpt/webauthn/createcredential-extensions.https.html [ Pass Timeout ]
 crbug.com/826936 external/wpt/webauthn/createcredential-passing.https.html [ Pass Timeout ]
-crbug.com/826936 external/wpt/webauthn/getcredential-badargs-rpid.https.html [ Pass Timeout ]
-crbug.com/826936 external/wpt/webauthn/getcredential-badargs-userverification.https.html [ Pass Timeout ]
-crbug.com/826936 external/wpt/webauthn/getcredential-extensions.https.html [ Pass Timeout ]
-crbug.com/826936 external/wpt/webauthn/getcredential-passing.https.html [ Pass Timeout ]
-crbug.com/826936 external/wpt/webauthn/getcredential-timeout.https.html [ Pass Timeout ]
 crbug.com/826936 external/wpt/webauthn/createcredential-pubkeycredparams.https.html [ Pass Timeout ]
 
+# Sheriff 2018-08-17
+crbug.com/826936 external/wpt/webauthn/createcredential-badargs-challenge.https.html [ Pass Timeout Failure ]
+crbug.com/826936 external/wpt/webauthn/getcredential-badargs-rpid.https.html [ Pass Timeout Failure ]
+crbug.com/826936 external/wpt/webauthn/getcredential-badargs-userverification.https.html [ Pass Timeout Failure ]
+crbug.com/826936 external/wpt/webauthn/getcredential-extensions.https.html [ Pass Timeout Failure ]
+crbug.com/826936 external/wpt/webauthn/getcredential-passing.https.html [ Pass Timeout Failure ]
+crbug.com/826936 external/wpt/webauthn/getcredential-timeout.https.html [ Pass Timeout Failure ]
+
 # WebRTC codec tests - software H.264 not present on webkit bot family
 crbug.com/840659 external/wpt/webrtc/protocol/video-codecs.https.html [ Pass Failure ]
 crbug.com/840659 virtual/webrtc-wpt-unified-plan/external/wpt/webrtc/protocol/video-codecs.https.html [ Pass Failure ]