Drop "only composite opacity animations when already in compositing mode".

Source/core/rendering/RenderLayerCompositor.cpp

Index: Source/core/rendering/RenderLayerCompositor.cpp
diff --git a/Source/core/rendering/RenderLayerCompositor.cpp b/Source/core/rendering/RenderLayerCompositor.cpp
index 09084ed814cd94e77220d8a4c2544b9a43907d86..0b6661cd3e53fef095f6c5c94d7da725802fd991 100644
--- a/Source/core/rendering/RenderLayerCompositor.cpp
+++ b/Source/core/rendering/RenderLayerCompositor.cpp
@@ -1709,13 +1709,10 @@ bool RenderLayerCompositor::requiresCompositingForAnimation(RenderObject* render
     if (!(m_compositingTriggers & ChromeClient::AnimationTrigger))
         return false;
 
-    if (!RuntimeEnabledFeatures::webAnimationsCSSEnabled()) {
-        // FIXME: Remove this condition once force-compositing-mode is enabled on all platforms.
-        bool shouldAccelerateOpacity = inCompositingMode();
-        return renderer->animation().isRunningAcceleratableAnimationOnRenderer(renderer, shouldAccelerateOpacity);
-    }
+    if (!RuntimeEnabledFeatures::webAnimationsCSSEnabled())
+        return renderer->animation().isRunningAcceleratableAnimationOnRenderer(renderer);
 
-    return shouldCompositeForActiveAnimations(*renderer, inCompositingMode());
+    return shouldCompositeForActiveAnimations(*renderer);
 }
 
 bool RenderLayerCompositor::requiresCompositingForTransition(RenderObject* renderer) const