[AnimationWorklet,BGPT] Mark animation worket test failing

This new test fails when using enable-blink-gen-property trees.
This is the intersection of two newly launching features and may block
the second one, whichever that happens to be.

Bug=861824

Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: Ib632eaa5377a7a5040597e8837dfa99e06883da0
Reviewed-on: https://chromium-review.googlesource.com/1129396Reviewed-by: Philip Rogers <pdr@chromium.org>
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Commit-Queue: Peter Mayo <petermayo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573419}

third_party/WebKit/LayoutTests/FlagExpectations/enable-blink-gen-property-trees

@@ -160,6 +160,8 @@ crbug.com/855702 virtual/threaded/animations/composited-filter-webkit-filter.htm
 crbug.com/855702 virtual/threaded/animations/img-element-transform.html [ Timeout Failure Pass ]
 crbug.com/855702 virtual/threaded/animations/compositor-independent-transform-cancel.html [ Failure ]
 
+crbug.com/861824 virtual/threaded/fast/animationworklet/animation-worklet-inside-iframe.html [ Failure ]
+
 # These scrollbar tests should pass.
 Bug(none) virtual/prefer_compositing_to_lcd_text/scrollbars/ [ Pass ]
 crbug.com/836912 compositing/rtl/rtl-absolute-overflow.html [ Failure ]