Bug 1611523 - Track the current layers id during the layer tree traversal in AsyncCompositionManager::ApplyAsyncContentTransformToTree(). r=hiro

Differential Revision: https://phabricator.services.mozilla.com/D61015

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

gfx/layers/composite/AsyncCompositionManager.cpp

@@ -896,6 +896,8 @@ bool AsyncCompositionManager::ApplyAsyncContentTransformToTree(
     Layer* aLayer, bool* aOutFoundRoot) {
   bool appliedTransform = false;
   std::stack<Maybe<ParentLayerIntRect>> stackDeferredClips;
+  std::stack<LayersId> layersIds;
+  layersIds.push(mCompositorBridge->RootLayerTreeId());
 
   // Maps layers to their ClipParts. The parts are not stored individually
   // on the layer, but during AlignFixedAndStickyLayers we need access to
@@ -908,6 +910,10 @@ bool AsyncCompositionManager::ApplyAsyncContentTransformToTree(
   ForEachNode<ForwardIterator>(
       aLayer,
       [&](Layer* layer) {
+        if (layer->AsRefLayer()) {
+          layersIds.push(layer->AsRefLayer()->GetReferentId());
+        }
+
         stackDeferredClips.push(Maybe<ParentLayerIntRect>());
 
         // If we encounter the async zoom container, find the corresponding
@@ -1274,6 +1280,11 @@ bool AsyncCompositionManager::ApplyAsyncContentTransformToTree(
             layers::ScrollbarLayerType::Thumb) {
           ApplyAsyncTransformToScrollbar(layer);
         }
+
+        if (layer->AsRefLayer()) {
+          MOZ_ASSERT(layersIds.size() > 1);
+          layersIds.pop();
+        }
       });
 
   return appliedTransform;