Mark two animation-type layout tests crash on Mac10.11 debug bot

TBR=smcgruer@chromium.org
NOTRY=true

Bug: 836185
Change-Id: I0f31be6d2638556bf6b734e6d8f03f1fd7eb4b19
Reviewed-on: https://chromium-review.googlesource.com/1025318Reviewed-by: Xida Chen <xidachen@chromium.org>
Commit-Queue: Xida Chen <xidachen@chromium.org>
Cr-Commit-Position: refs/heads/master@{#553053}

third_party/WebKit/LayoutTests/TestExpectations

@@ -4111,3 +4111,7 @@ crbug.com/834446 [ Linux ] http/tests/misc/performance-memory.html [ Pass Failur
 # Sheriff 2018-04-23
 crbug.com/833331 [ Win10 ] inspector-protocol/page/pageNavigateToFragment.js [ Pass Failure ]
 crbug.com/831796 virtual/mouseevent_fractional/fast/events/autoscroll-in-textfield.html [ Failure Pass ]
+
+# Sheriff 2018-04-24
+crbug.com/836185 [ Mac10.11 Debug ] external/wpt/web-animations/animation-model/animation-types/addition-per-property.html [ Crash ]
+crbug.com/836185 [ Mac10.11 Debug ] external/wpt/web-animations/animation-model/animation-types/interpolation-per-property.html [ Crash ]