Bug 1641085 Part 2 - Add APIs to manipulate overflow containers list. r=mats

Not all APIs added in this patch are used immediately, but for the sake of
completeness, they are all added.

Their document will be updated in Part 3 after adding the relevant APIs for
ExcessOverflowContainersProperty().

nsContainerFrame::DrainExcessOverflowContainersList() has several calls to set
OverflowContainersProperty() whose life cycle need special attention. We will
deal with them later in Part 4.

Differential Revision: https://phabricator.services.mozilla.com/D88456

layout/generic/nsBlockFrame.cpp

@@ -5169,7 +5169,7 @@ bool nsBlockFrame::DrainOverflowLines() {
       // prev-in-flow. We'll append these to mFrames to ensure the continuations
       // are ordered.
       auto HasOverflowContainers = [this]() -> bool {
-        return GetPropTableFrames(OverflowContainersProperty()) ||
+        return GetOverflowContainers() ||
                GetPropTableFrames(ExcessOverflowContainersProperty());
       };
       nsFrameList ocContinuations;

layout/generic/nsContainerFrame.cpp

@@ -301,7 +301,7 @@ const nsFrameList& nsContainerFrame::GetChildList(ChildListID aListID) const {
       return list ? *list : nsFrameList::EmptyList();
     }
     case kOverflowContainersList: {
-      nsFrameList* list = GetPropTableFrames(OverflowContainersProperty());
+      nsFrameList* list = GetOverflowContainers();
       return list ? *list : nsFrameList::EmptyList();
     }
     case kExcessOverflowContainersList: {
@@ -1397,7 +1397,7 @@ void nsContainerFrame::ReflowOverflowContainerChildren(
 
 void nsContainerFrame::DisplayOverflowContainers(
     nsDisplayListBuilder* aBuilder, const nsDisplayListSet& aLists) {
-  nsFrameList* overflowconts = GetPropTableFrames(OverflowContainersProperty());
+  nsFrameList* overflowconts = GetOverflowContainers();
   if (overflowconts) {
     for (nsIFrame* frame : *overflowconts) {
       BuildDisplayListForChild(aBuilder, frame, aLists);
@@ -1439,7 +1439,7 @@ nsresult nsContainerFrame::StealFrame(nsIFrame* aChild) {
   if (!mFrames.ContainsFrame(aChild)) {
     nsFrameList* list = GetOverflowFrames();
     if (!list || !list->ContainsFrame(aChild)) {
-      list = GetProperty(OverflowContainersProperty());
+      list = GetOverflowContainers();
       if (!list || !list->ContainsFrame(aChild)) {
         list = GetProperty(ExcessOverflowContainersProperty());
         MOZ_ASSERT(list && list->ContainsFrame(aChild),
@@ -1752,8 +1752,7 @@ bool nsContainerFrame::PushIncompleteChildren(
     // overflowIncompleteList into that list. Otherwise, merge it into our
     // excess overflow containers list, to be drained by our next-in-flow.
     auto* nif = static_cast<nsContainerFrame*>(GetNextInFlow());
-    nsFrameList* oc =
-        nif ? nif->GetPropTableFrames(OverflowContainersProperty()) : nullptr;
+    nsFrameList* oc = nif ? nif->GetOverflowContainers() : nullptr;
     if (oc) {
       ReparentFrames(overflowIncompleteList, this, nif);
       MergeSortedFrameLists(*oc, overflowIncompleteList, GetContent());
@@ -1839,8 +1838,7 @@ void nsContainerFrame::NormalizeChildLists() {
           f = next;
         }
         if (overflowContainers->IsEmpty()) {
-          (void)TakeProperty(OverflowContainersProperty());
-          overflowContainers->Delete(PresShell());
+          DestroyOverflowContainers();
         }
         MergeSortedExcessOverflowContainers(moveToEOC);
       }
@@ -2246,8 +2244,7 @@ bool nsContainerFrame::DrainAndMergeSelfOverflowList() {
 
 nsFrameList* nsContainerFrame::DrainExcessOverflowContainersList(
     ChildFrameMerger aMergeFunc) {
-  nsFrameList* overflowContainers =
-      GetPropTableFrames(OverflowContainersProperty());
+  nsFrameList* overflowContainers = GetOverflowContainers();
 
   NS_ASSERTION(!(overflowContainers && GetPrevInFlow() &&
                  static_cast<nsContainerFrame*>(GetPrevInFlow())
@@ -2936,8 +2933,7 @@ void nsOverflowContinuationTracker::SetupOverflowContList() {
   nsContainerFrame* nif =
       static_cast<nsContainerFrame*>(mParent->GetNextInFlow());
   if (nif) {
-    mOverflowContList =
-        nif->GetPropTableFrames(nsContainerFrame::OverflowContainersProperty());
+    mOverflowContList = nif->GetOverflowContainers();
     if (mOverflowContList) {
       mParent = nif;
       SetUpListWalker();
@@ -3144,8 +3140,7 @@ void nsOverflowContinuationTracker::EndFinish(nsIFrame* aChild) {
   nsFrameList* eoc = mParent->GetProperty(
       nsContainerFrame::ExcessOverflowContainersProperty());
   if (eoc != mOverflowContList) {
-    nsFrameList* oc = static_cast<nsFrameList*>(
-        mParent->GetProperty(nsContainerFrame::OverflowContainersProperty()));
+    nsFrameList* oc = mParent->GetOverflowContainers();
     if (oc != mOverflowContList) {
       // mOverflowContList was deleted
       mPrevOverflowCont = nullptr;
@@ -3204,7 +3199,7 @@ void nsContainerFrame::SanityCheckChildListsBeforeReflow() const {
   // should be one of our children or be null.
   const auto* pif = static_cast<nsContainerFrame*>(GetPrevInFlow());
   if (pif) {
-    const nsFrameList* oc = GetPropTableFrames(OverflowContainersProperty());
+    const nsFrameList* oc = GetOverflowContainers();
     const nsFrameList* eoc =
         GetPropTableFrames(ExcessOverflowContainersProperty());
     const nsFrameList* pifEOC =

layout/generic/nsContainerFrame.h

@@ -541,11 +541,17 @@ class nsContainerFrame : public nsSplittableFrame {
    * still owned by this frame.  A non-null return value indicates that the
    * list is nonempty.
    */
-  nsFrameList* GetOverflowFrames() const {
+  [[nodiscard]] nsFrameList* GetOverflowFrames() const {
     nsFrameList* list = GetProperty(OverflowProperty());
     NS_ASSERTION(!list || !list->IsEmpty(), "Unexpected empty overflow list");
     return list;
   }
+  [[nodiscard]] nsFrameList* GetOverflowContainers() const {
+    nsFrameList* list = GetProperty(OverflowContainersProperty());
+    NS_ASSERTION(!list || !list->IsEmpty(),
+                 "Unexpected empty overflow containers list");
+    return list;
+  }
 
   /**
    * As GetOverflowFrames, but removes the overflow frames property.  The
@@ -560,6 +566,11 @@ class nsContainerFrame : public nsSplittableFrame {
     NS_ASSERTION(!list || !list->IsEmpty(), "Unexpected empty overflow list");
     return list;
   }
+  [[nodiscard]] nsFrameList* StealOverflowContainers() {
+    nsFrameList* list = TakeProperty(OverflowContainersProperty());
+    NS_ASSERTION(!list || !list->IsEmpty(), "Unexpected empty overflow list");
+    return list;
+  }
 
   /**
    * Set the overflow list.  aOverflowFrames must not be an empty list.
@@ -569,6 +580,15 @@ class nsContainerFrame : public nsSplittableFrame {
     SetProperty(OverflowProperty(),
                 new (PresShell()) nsFrameList(std::move(aOverflowFrames)));
   }
+  void SetOverflowContainers(nsFrameList&& aOverflowContainers) {
+    MOZ_ASSERT(aOverflowContainers.NotEmpty(), "Shouldn't set an empty list!");
+    MOZ_ASSERT(!GetProperty(OverflowContainersProperty()),
+               "Shouldn't override existing list!");
+    MOZ_ASSERT(IsFrameOfType(nsIFrame::eCanContainOverflowContainers),
+               "This type of frame can't have overflow containers!");
+    SetProperty(OverflowContainersProperty(),
+                new (PresShell()) nsFrameList(std::move(aOverflowContainers)));
+  }
 
   /**
    * Destroy the overflow list, which must be empty.
@@ -578,6 +598,11 @@ class nsContainerFrame : public nsSplittableFrame {
     MOZ_ASSERT(list && list->IsEmpty());
     list->Delete(PresShell());
   }
+  void DestroyOverflowContainers() {
+    nsFrameList* list = TakeProperty(OverflowContainersProperty());
+    MOZ_ASSERT(list && list->IsEmpty());
+    list->Delete(PresShell());
+  }
 
   /**
    * Moves any frames on both the prev-in-flow's overflow list and the