Bug 1473136: Cache mNeedsActiveLayer once for nsDisplayOpacity. r=mattwoodrow

layout/generic/nsFrame.cpp

@@ -2952,6 +2952,8 @@ nsIFrame::BuildDisplayListForStackingContext(nsDisplayListBuilder* aBuilder,
     aBuilder->EnterSVGEffectsContents(&hoistedScrollInfoItemsStorage);
   }
 
+
+  bool needsActiveOpacityLayer = false;
   // We build an opacity item if it's not going to be drawn by SVG content, or
   // SVG effects. SVG effects won't handle the opacity if we want an active
   // layer (for async animations), see
@@ -2959,7 +2961,7 @@ nsIFrame::BuildDisplayListForStackingContext(nsDisplayListBuilder* aBuilder,
   // nsSVGIntegrationsUtils::PaintFilter.
   bool useOpacity = HasVisualOpacity(effectSet) &&
                     !nsSVGUtils::CanOptimizeOpacity(this) &&
-                    (!usingSVGEffects || nsDisplayOpacity::NeedsActiveLayer(aBuilder, this));
+                    ((needsActiveOpacityLayer = nsDisplayOpacity::NeedsActiveLayer(aBuilder, this)) || !usingSVGEffects);
   bool useBlendMode = effects->mMixBlendMode != NS_STYLE_BLEND_NORMAL;
   bool useStickyPosition = disp->mPosition == NS_STYLE_POSITION_STICKY &&
     IsScrollFrameActive(aBuilder,
@@ -3259,9 +3261,10 @@ nsIFrame::BuildDisplayListForStackingContext(nsDisplayListBuilder* aBuilder,
     // all descendant content, but some should not be clipped.
     DisplayListClipState::AutoSaveRestore opacityClipState(aBuilder);
     resultList.AppendToTop(
-        MakeDisplayItem<nsDisplayOpacity>(aBuilder, this, &resultList,
+      MakeDisplayItem<nsDisplayOpacity>(aBuilder, this, &resultList,
                                         containerItemASR,
-                                        opacityItemForEventsAndPluginsOnly));
+                                        opacityItemForEventsAndPluginsOnly,
+                                        needsActiveOpacityLayer));
     if (aCreatedContainerItem) {
       *aCreatedContainerItem = true;
     }

layout/painting/nsDisplayList.cpp

@@ -6237,10 +6237,12 @@ nsresult nsDisplayWrapper::WrapListsInPlace(nsDisplayListBuilder* aBuilder,
 nsDisplayOpacity::nsDisplayOpacity(nsDisplayListBuilder* aBuilder,
                                    nsIFrame* aFrame, nsDisplayList* aList,
                                    const ActiveScrolledRoot* aActiveScrolledRoot,
-                                   bool aForEventsAndPluginsOnly)
+                                   bool aForEventsAndPluginsOnly,
+                                   bool aNeedsActiveLayer)
     : nsDisplayWrapList(aBuilder, aFrame, aList, aActiveScrolledRoot, true)
     , mOpacity(aFrame->StyleEffects()->mOpacity)
     , mForEventsAndPluginsOnly(aForEventsAndPluginsOnly)
+    , mNeedsActiveLayer(aNeedsActiveLayer)
     , mChildOpacityState(ChildOpacityState::Unknown)
 {
   MOZ_COUNT_CTOR(nsDisplayOpacity);
@@ -6434,7 +6436,7 @@ nsDisplayOpacity::ShouldFlattenAway(nsDisplayListBuilder* aBuilder)
     return false;
   }
 
-  if (NeedsActiveLayer(aBuilder, mFrame) || mOpacity == 0.0) {
+  if (mNeedsActiveLayer || mOpacity == 0.0) {
     // If our opacity is zero then we'll discard all descendant display items
     // except for layer event regions, so there's no point in doing this
     // optimization (and if we do do it, then invalidations of those descendants
@@ -6464,7 +6466,7 @@ nsDisplayOpacity::GetLayerState(nsDisplayListBuilder* aBuilder,
     return LAYER_INACTIVE;
   }
 
-  if (NeedsActiveLayer(aBuilder, mFrame)) {
+  if (mNeedsActiveLayer) {
     // Returns LAYER_ACTIVE_FORCE to avoid flatterning the layer for async
     // animations.
     return LAYER_ACTIVE_FORCE;

layout/painting/nsDisplayList.h

@@ -5121,13 +5121,15 @@ public:
   nsDisplayOpacity(nsDisplayListBuilder* aBuilder, nsIFrame* aFrame,
                    nsDisplayList* aList,
                    const ActiveScrolledRoot* aActiveScrolledRoot,
-                   bool aForEventsAndPluginsOnly);
+                   bool aForEventsAndPluginsOnly,
+                   bool aNeedsActiveLayer);
 
   nsDisplayOpacity(nsDisplayListBuilder* aBuilder,
                    const nsDisplayOpacity& aOther)
     : nsDisplayWrapList(aBuilder, aOther)
     , mOpacity(aOther.mOpacity)
     , mForEventsAndPluginsOnly(aOther.mForEventsAndPluginsOnly)
+    , mNeedsActiveLayer(aOther.mNeedsActiveLayer)
     , mChildOpacityState(ChildOpacityState::Unknown)
   {
     // We should not try to merge flattened opacities.
@@ -5225,6 +5227,7 @@ private:
     // Opacity is applied to our children.
     Applied
   };
+  bool mNeedsActiveLayer : 1;
 #ifndef __GNUC__
   ChildOpacityState mChildOpacityState : 2;
 #else