--- a/gfx/layers/apz/src/APZCTreeManager.cpp
+++ b/gfx/layers/apz/src/APZCTreeManager.cpp
@@ -448,28 +448,28 @@ APZCTreeManager::PrepareNodeForLayer(con
 
     // For testing, log the parent scroll id of every APZC that has a
     // parent. This allows test code to reconstruct the APZC tree.
     // Note that we currently only do this for APZCs in the layer tree
     // that originated the update, because the only identifying information
     // we are logging about APZCs is the scroll id, and otherwise we could
     // confuse APZCs from different layer trees with the same scroll id.
     if (aLayersId == aState.mOriginatingLayersId) {
-      if (apzc->IsRootForLayersId()) {
+      if (apzc->HasNoParentWithSameLayersId()) {
         aState.mPaintLogger.LogTestData(aMetrics.GetScrollId(),
-            "isRootForLayersId", true);
+            "hasNoParentWithSameLayersId", true);
       } else {
         MOZ_ASSERT(apzc->GetParent());
         aState.mPaintLogger.LogTestData(aMetrics.GetScrollId(),
             "parentScrollId", apzc->GetParent()->GetGuid().mScrollId);
       }
     }
 
     if (newApzc) {
-      if (apzc->IsRootForLayersId()) {
+      if (apzc->HasNoParentWithSameLayersId()) {
         // If we just created a new apzc that is the root for its layers ID, then
         // we need to update its zoom constraints which might have arrived before this
         // was created
         ZoomConstraints constraints;
         if (state->mController->GetRootZoomConstraints(&constraints)) {
           apzc->UpdateZoomConstraints(constraints);
         }
       } else {
@@ -1035,34 +1035,34 @@ APZCTreeManager::UpdateZoomConstraints(c
                                        const ZoomConstraints& aConstraints)
 {
   MonitorAutoLock lock(mTreeLock);
   nsRefPtr<HitTestingTreeNode> node = GetTargetNode(aGuid, nullptr);
   MOZ_ASSERT(!node || node->GetApzc()); // any node returned must have an APZC
 
   // For a given layers id, non-root APZCs inherit the zoom constraints
   // of their root.
-  if (node && node->GetApzc()->IsRootForLayersId()) {
+  if (node && node->GetApzc()->HasNoParentWithSameLayersId()) {
     UpdateZoomConstraintsRecursively(node.get(), aConstraints);
   }
 }
 
 void
 APZCTreeManager::UpdateZoomConstraintsRecursively(HitTestingTreeNode* aNode,
                                                   const ZoomConstraints& aConstraints)
 {
   mTreeLock.AssertCurrentThreadOwns();
 
   if (aNode->IsPrimaryHolder()) {
     MOZ_ASSERT(aNode->GetApzc());
     aNode->GetApzc()->UpdateZoomConstraints(aConstraints);
   }
   for (HitTestingTreeNode* child = aNode->GetLastChild(); child; child = child->GetPrevSibling()) {
     // We can have subtrees with their own layers id - leave those alone.
-    if (child->GetApzc() && child->GetApzc()->IsRootForLayersId()) {
+    if (child->GetApzc() && child->GetApzc()->HasNoParentWithSameLayersId()) {
       continue;
     }
     UpdateZoomConstraintsRecursively(child, aConstraints);
   }
 }
 
 void
 APZCTreeManager::FlushRepaintsToClearScreenToGeckoTransform()
@@ -1339,17 +1339,17 @@ APZCTreeManager::BuildOverscrollHandoffC
   // but do not follow the expected layer tree structure. If there are no
   // scroll parent links we just walk up the tree to find the scroll parent.
   OverscrollHandoffChain* result = new OverscrollHandoffChain;
   AsyncPanZoomController* apzc = aInitialTarget;
   while (apzc != nullptr) {
     result->Add(apzc);
 
     if (apzc->GetScrollHandoffParentId() == FrameMetrics::NULL_SCROLL_ID) {
-      if (!apzc->IsRootForLayersId()) {
+      if (!apzc->HasNoParentWithSameLayersId()) {
         // This probably indicates a bug or missed case in layout code
         NS_WARNING("Found a non-root APZ with no handoff parent");
       }
       apzc = apzc->GetParent();
       continue;
     }
 
     // Guard against a possible infinite-loop condition. If we hit this, the
@@ -1357,17 +1357,17 @@ APZCTreeManager::BuildOverscrollHandoffC
     MOZ_ASSERT(apzc->GetScrollHandoffParentId() != apzc->GetGuid().mScrollId);
 
     // Find the AsyncPanZoomController instance with a matching layersId and
     // the scroll id that matches apzc->GetScrollHandoffParentId(). To do this
     // search the subtree with the same layersId for the apzc with the specified
     // scroll id.
     AsyncPanZoomController* scrollParent = nullptr;
     AsyncPanZoomController* parent = apzc;
-    while (!parent->IsRootForLayersId()) {
+    while (!parent->HasNoParentWithSameLayersId()) {
       parent = parent->GetParent();
       // While walking up to find the root of the subtree, if we encounter the
       // handoff parent, we don't actually need to do the search so we can
       // just abort here.
       if (parent->GetGuid().mScrollId == apzc->GetScrollHandoffParentId()) {
         scrollParent = parent;
         break;
       }
@@ -1700,16 +1700,16 @@ APZCTreeManager::CommonAncestor(AsyncPan
   return ancestor.forget();
 }
 
 already_AddRefed<AsyncPanZoomController>
 APZCTreeManager::RootAPZCForLayersId(AsyncPanZoomController* aApzc) const
 {
   MonitorAutoLock lock(mTreeLock);
   nsRefPtr<AsyncPanZoomController> apzc = aApzc;
-  while (apzc && !apzc->IsRootForLayersId()) {
+  while (apzc && !apzc->HasNoParentWithSameLayersId()) {
     apzc = apzc->GetParent();
   }
   return apzc.forget();
 }
 
 }
 }

--- a/gfx/layers/apz/src/AsyncPanZoomController.h
+++ b/gfx/layers/apz/src/AsyncPanZoomController.h
@@ -894,19 +894,20 @@ public:
     mParent = aParent;
   }
 
   AsyncPanZoomController* GetParent() const {
     return mParent;
   }
 
   /* Returns true if there is no APZC higher in the tree with the same
-   * layers id.
+   * layers id. Deprecated. New code shouldn't use this. Old code should be
+   * updated to not use this.
    */
-  bool IsRootForLayersId() const {
+  bool HasNoParentWithSameLayersId() const {
     return !mParent || (mParent->mLayersId != mLayersId);
   }
 
 private:
   // This is a raw pointer to avoid introducing a reference cycle between
   // AsyncPanZoomController and APZCTreeManager. Since these objects don't
   // live on the main thread, we can't use the cycle collector with them.
   // The APZCTreeManager owns the lifetime of the APZCs, so nulling this

--- a/gfx/layers/apz/test/apz_test_utils.js
+++ b/gfx/layers/apz/test/apz_test_utils.js
@@ -86,16 +86,16 @@ function addRoot(root, id) {
 // content process that triggered the paint, is reconstructed (as
 // the APZ test data only contains information abot this subtree).
 function buildApzcTree(paint) {
   // The APZC tree can potentially have multiple root nodes,
   // so we invent a node that is the parent of all roots.
   // This 'root' does not correspond to an APZC.
   var root = makeNode(-1);
   for (var scrollId in paint) {
-    if ("isRootForLayersId" in paint[scrollId]) {
+    if ("hasNoParentWithSameLayersId" in paint[scrollId]) {
       addRoot(root, scrollId);
     } else if ("parentScrollId" in paint[scrollId]) {
       addLink(root, scrollId, paint[scrollId]["parentScrollId"]);
     }
   }
   return root;
 }