ContainerNode: Avoid dynamic allocation of HeapVector in ChildrenChange

Bug: 1154667
Change-Id: I65fe8ef14793a65571362b49cc5c7250f43cd30c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2567168Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#833378}

third_party/blink/renderer/core/dom/character_data.cc

@@ -234,7 +234,7 @@ void CharacterData::DidModifyData(const String& old_data, UpdateSource source) {
         this,
         previousSibling(),
         nextSibling(),
-        nullptr};
+        {}};
     parentNode()->ChildrenChanged(change);
   }
 

third_party/blink/renderer/core/dom/container_node.cc

@@ -814,11 +814,8 @@ void ContainerNode::RemoveChildren(SubtreeModificationAction action) {
     GetDocument().NodeChildrenWillBeRemoved(*this);
   }
 
-  HeapVector<Member<Node>>* removed_nodes = nullptr;
-  if (ChildrenChangedAllChildrenRemovedNeedsList()) {
-    removed_nodes =
-        MakeGarbageCollected<HeapVector<Member<Node>>>(CountChildren());
-  }
+  HeapVector<Member<Node>> removed_nodes;
+  const bool children_changed = ChildrenChangedAllChildrenRemovedNeedsList();
   {
     HTMLFrameOwnerElement::PluginDisposeSuspendScope suspend_plugin_dispose;
     TreeOrderedMap::RemoveScope tree_remove_scope;
@@ -831,8 +828,8 @@ void ContainerNode::RemoveChildren(SubtreeModificationAction action) {
       while (Node* child = first_child_) {
         RemoveBetween(nullptr, child->nextSibling(), *child);
         NotifyNodeRemoved(*child);
-        if (removed_nodes)
-          removed_nodes->push_back(child);
+        if (children_changed)
+          removed_nodes.push_back(child);
       }
     }
 
@@ -841,7 +838,7 @@ void ContainerNode::RemoveChildren(SubtreeModificationAction action) {
                              nullptr,
                              nullptr,
                              nullptr,
-                             removed_nodes};
+                             std::move(removed_nodes)};
     ChildrenChanged(change);
   }
 

third_party/blink/renderer/core/dom/container_node.h

@@ -318,7 +318,7 @@ class CORE_EXPORT ContainerNode : public Node {
                                &node,
                                unchanged_previous,
                                unchanged_next,
-                               nullptr};
+                               {}};
       return change;
     }
 
@@ -333,7 +333,7 @@ class CORE_EXPORT ContainerNode : public Node {
                                &node,
                                previous_sibling,
                                next_sibling,
-                               nullptr};
+                               {}};
       return change;
     }
 
@@ -367,9 +367,9 @@ class CORE_EXPORT ContainerNode : public Node {
     //  - nextSibling of the last inserted node after multiple node insertion.
     Node* sibling_after_change = nullptr;
     // List of removed nodes for ChildrenChangeType::kAllChildrenRemoved.
-    // This is available only if ChildrenChangedAllChildrenRemovedNeedsList()
-    // returns true.
-    HeapVector<Member<Node>>* removed_nodes;
+    // Only populated if ChildrenChangedAllChildrenRemovedNeedsList() returns
+    // true.
+    HeapVector<Member<Node>> removed_nodes;
   };
 
   // Notifies the node that it's list of children have changed (either by adding

third_party/blink/renderer/core/html/forms/html_opt_group_element.cc

@@ -96,8 +96,7 @@ void HTMLOptGroupElement::ChildrenChanged(const ChildrenChange& change) {
     if (auto* option = DynamicTo<HTMLOptionElement>(change.sibling_changed))
       select->OptionRemoved(*option);
   } else if (change.type == ChildrenChangeType::kAllChildrenRemoved) {
-    DCHECK(change.removed_nodes);
-    for (Node* node : *change.removed_nodes) {
+    for (Node* node : change.removed_nodes) {
       if (auto* option = DynamicTo<HTMLOptionElement>(node))
         select->OptionRemoved(*option);
     }

third_party/blink/renderer/core/html/forms/html_select_element.cc

@@ -709,8 +709,7 @@ void HTMLSelectElement::ChildrenChanged(const ChildrenChange& change) {
         OptionRemoved(child_option);
     }
   } else if (change.type == ChildrenChangeType::kAllChildrenRemoved) {
-    DCHECK(change.removed_nodes);
-    for (Node* node : *change.removed_nodes) {
+    for (Node* node : change.removed_nodes) {
       if (auto* option = DynamicTo<HTMLOptionElement>(node)) {
         OptionRemoved(*option);
       } else if (auto* optgroup = DynamicTo<HTMLOptGroupElement>(node)) {