Add an expectation for an incoming test to unblock import

The test behaves differently on try bots and CQ bots so it can't be
rebaselined automatically.

TBR=raphael.kubo.da.costa@intel.com

No-Try: True
Bug: 857271
Change-Id: I8a1fe9f524cca6cf73370b76bba3d64557ab33f8
Reviewed-on: https://chromium-review.googlesource.com/1117842
Commit-Queue: Robert Ma <robertma@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570952}

third_party/WebKit/LayoutTests/TestExpectations

@@ -2795,6 +2795,8 @@ crbug.com/849859 external/wpt/css/css-animations/CSSAnimation-pausing.tentative.
 crbug.com/849859 external/wpt/css/css-animations/Element-getAnimations-dynamic-changes.tentative.html [ Failure ]
 crbug.com/849859 external/wpt/web-animations/timing-model/animations/pausing-an-animation.html [ Failure ]
 
+crbug.com/857271 external/wpt/encrypted-media/clearkey-mp4-playback-temporary-clear-encrypted-segmented.https.html [ Failure Timeout ]
+
 # ====== New tests from wpt-importer added here ======
 crbug.com/626703 virtual/outofblink-cors/external/wpt/fetch/api/request/request-keepalive-quota.html?include=slow-2 [ Timeout ]
 crbug.com/626703 external/wpt/fetch/api/request/request-keepalive-quota.html?include=slow-2 [ Timeout ]