Bug 1567889 - Part 2: Avoid will-change budget lookups if the frame does not have the will-change bit set r=mattwoodrow

Differential Revision: https://phabricator.services.mozilla.com/D38852

--HG--
extra : moz-landing-system : lando

layout/generic/nsFrame.cpp

@@ -3895,7 +3895,6 @@ void nsIFrame::BuildDisplayListForChild(nsDisplayListBuilder* aBuilder,
   }
 
   nsIFrame* child = aChild;
-  aBuilder->RemoveFromWillChangeBudget(child);
 
   const bool isPaintingToWindow = aBuilder->IsPaintingToWindow();
   const bool doingShortcut =
@@ -3904,6 +3903,8 @@ void nsIFrame::BuildDisplayListForChild(nsDisplayListBuilder* aBuilder,
       // Animations may change the stacking context state.
       !(child->MayHaveTransformAnimation() || child->MayHaveOpacityAnimation());
 
+  aBuilder->RemoveFromWillChangeBudget(child);
+
   if (StaticPrefs::layout_css_scroll_anchoring_highlight()) {
     if (child->FirstContinuation()->IsScrollAnchor()) {
       nsRect bounds = child->GetContentRectRelativeToSelf() +

layout/painting/nsDisplayList.cpp

@@ -2549,6 +2549,11 @@ bool nsDisplayListBuilder::IsInWillChangeBudget(nsIFrame* aFrame,
 }
 
 void nsDisplayListBuilder::RemoveFromWillChangeBudget(nsIFrame* aFrame) {
+  if (!aFrame->MayHaveWillChangeBudget()) {
+    MOZ_ASSERT(!mWillChangeBudgetSet.Contains(aFrame));
+    return;
+  }
+
   FrameWillChangeBudget* frameBudget = mWillChangeBudgetSet.GetValue(aFrame);
 
   if (!frameBudget) {