Mark transitions/opacity-transition-zindex.html as passing

This patch removes a bad baseline added in https://crrev.com/614470
and marks the test as passing.

Bug: 912380
Change-Id: Ia4cab4002371ff23e75c82f717a12689c7dfdf2a
Reviewed-on: https://chromium-review.googlesource.com/c/1367931
Commit-Queue: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614734}

third_party/blink/web_tests/TestExpectations

@@ -360,9 +360,6 @@ Bug(none) http/tests/devtools/layers/layer-sticky-position-constraint-get.js [ S
 Bug(none) inspector-protocol/layers/get-layers.js [ Skip ]
 
 # ==== Regressions introduced by BlinkGenPropertyTrees =====
-# Opacity not applied to descendant of animated filter node.
-crbug.com/912380 transitions/opacity-transition-zindex.html [ Failure ]
-crbug.com/912380 virtual/threaded/transitions/opacity-transition-zindex.html [ Failure ]
 # Reflection / mask ordering issue
 crbug.com/767318 compositing/reflections/nested-reflection-mask-change.html [ Failure ]
 # Incorrect scrollbar invalidation.