[BlinkPropertyTrees] Shortcut AnimateLayers on main

These can cause animations to attempt to update elements which are no longer in
the property tree. It's all duplicate work to what will happen on CC and be
pushed back.

BUG=762717

Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I92188f6a61b73274eb9ef1a4608585ae64e56683
Reviewed-on: https://chromium-review.googlesource.com/1091504
Commit-Queue: Peter Mayo <petermayo@chromium.org>
Reviewed-by: Majid Valipour <majidvp@chromium.org>
Reviewed-by: Robert Flack <flackr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#568065}

cc/trees/layer_tree_host.cc

@@ -911,6 +911,14 @@ void LayerTreeHost::UpdateBrowserControlsState(
 }
 
 void LayerTreeHost::AnimateLayers(base::TimeTicks monotonic_time) {
+  // We do not need to animate on the main thread in this case because all
+  // relevant changes will be processed on the compositor thread, or proxy,
+  // and propagated back to the correct trees.
+  // TODO(majidvp): We should be able to eliminate this in the non-
+  // slimming path and will do so in a follow up. (762717)
+  if (IsUsingLayerLists())
+    return;
+
   std::unique_ptr<MutatorEvents> events = mutator_host_->CreateEvents();
 
   if (mutator_host_->TickAnimations(monotonic_time,

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

@@ -146,18 +146,10 @@ Bug(none) virtual/threaded/transitions/ [ Pass ]
 Bug(none) virtual/threaded/fast/animationworklet/ [ Pass ]
 crbug.com/836897 transitions/opacity-transform-transitions-inside-iframe.html [ Timeout ]
 crbug.com/836897 transitions/transition-end-event-destroy-iframe.html [ Timeout ]
-crbug.com/836897 virtual/threaded/animations/direction-and-fill/fill-mode-forwards2.html [ Crash ]
 crbug.com/836897 virtual/threaded/animations/composited-filter-webkit-filter.html [ Failure ]
-crbug.com/836897 virtual/threaded/transitions/composited-with-hit-testing.html [ Crash Failure Pass ]
-crbug.com/836897 virtual/threaded/animations/KeyframeEffect-composited-animation.html [ Crash Failure Pass ]
 crbug.com/836897 virtual/threaded/animations/img-element-transform.html [ Timeout Failure Pass ]
 crbug.com/836897 virtual/threaded/animations/compositor-independent-transform-cancel.html [ Failure ]
-crbug.com/836897 virtual/threaded/animations/composited-animation-independent-transform-cancel.html [ Crash Failure Pass ]
 crbug.com/836897 virtual/threaded/fast/animationworklet/animation-worklet-animator-animate.html [ Failure ]
-crbug.com/836897 virtual/threaded/fast/animationworklet/worklet-animation-style-update.html [ Crash Failure Pass ]
-crbug.com/836897 virtual/threaded/animations/inline-block-transform.html [ Crash Failure Pass ]
-crbug.com/836897 virtual/threaded/animations/start-time-grouping.html [ Crash Failure Pass ]
-crbug.com/836897 virtual/threaded/animations/element-animate-positive-delay.html [ Crash Failure Pass ]
 crbug.com/836897 virtual/threaded/transitions/opacity-transform-transitions-inside-iframe.html [ Timeout ]
 crbug.com/836897 virtual/threaded/transitions/transition-end-event-destroy-iframe.html [ Timeout ]
 crbug.com/836897 virtual/threaded/fast/animationworklet/animation-worklet-animator-with-options.html [ Failure ]