Move LayoutBoxRareData to Oilpan

https://docs.google.com/document/d/1AJ1XCtiYbaw64KhPX_a_TiNDOqeYV-MO30I1C-8VzPk/edit#heading=h.p9sgjwxtsd3c

Change-Id: Ic3a1ae8c3cc4a0f473c3309e2ef0de47db40bf6f
Bug: 1030176
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1974727Reviewed-by: Kentaro Hara <haraken@chromium.org>
Commit-Queue: Navid Zolghadr <nzolghadr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#726273}

third_party/blink/renderer/core/layout/layout_box.cc

@@ -108,7 +108,8 @@ struct SameSizeAsLayoutBox : public LayoutBoxModelObject {
   LayoutUnit intrinsic_content_logical_height;
   LayoutRectOutsets margin_box_outsets;
   LayoutUnit preferred_logical_width[2];
-  void* pointers[5];
+  void* pointers[4];
+  Persistent<void*> rare_data;
 };
 
 static_assert(sizeof(LayoutBox) == sizeof(SameSizeAsLayoutBox),
@@ -135,6 +136,10 @@ LayoutBoxRareData::LayoutBoxRareData()
       snap_container_(nullptr),
       snap_areas_(nullptr) {}
 
+void LayoutBoxRareData::Trace(Visitor* visitor) {
+  visitor->Trace(layout_child_);
+}
+
 LayoutBox::LayoutBox(ContainerNode* node)
     : LayoutBoxModelObject(node),
       intrinsic_content_logical_height_(-1),

third_party/blink/renderer/core/layout/layout_box.h

@@ -66,12 +66,12 @@ enum ShouldComputePreferred { kComputeActual, kComputePreferred };
 
 using SnapAreaSet = HashSet<LayoutBox*>;
 
-struct LayoutBoxRareData {
-  USING_FAST_MALLOC(LayoutBoxRareData);
-
+struct LayoutBoxRareData final : public GarbageCollected<LayoutBoxRareData> {
  public:
   LayoutBoxRareData();
 
+  void Trace(Visitor* visitor);
+
   // For spanners, the spanner placeholder that lays us out within the multicol
   // container.
   LayoutMultiColumnSpannerPlaceholder* spanner_placeholder_;
@@ -115,7 +115,7 @@ struct LayoutBoxRareData {
   // Used by CSSLayoutDefinition::Instance::Layout. Represents the script
   // object for this box that web developers can query style, and perform
   // layout upon. Only created if IsCustomItem() is true.
-  Persistent<CustomLayoutChild> layout_child_;
+  Member<CustomLayoutChild> layout_child_;
 
   DISALLOW_COPY_AND_ASSIGN(LayoutBoxRareData);
 };
@@ -1768,8 +1768,8 @@ class CORE_EXPORT LayoutBox : public LayoutBoxModelObject {
 
   LayoutBoxRareData& EnsureRareData() {
     if (!rare_data_)
-      rare_data_ = std::make_unique<LayoutBoxRareData>();
-    return *rare_data_.get();
+      rare_data_ = MakeGarbageCollected<LayoutBoxRareData>();
+    return *rare_data_.Get();
   }
 
   bool LogicalHeightComputesAsNone(SizeType) const;
@@ -1894,7 +1894,7 @@ class CORE_EXPORT LayoutBox : public LayoutBoxModelObject {
     wtf_size_t first_fragment_item_index_;
   };
 
-  std::unique_ptr<LayoutBoxRareData> rare_data_;
+  Persistent<LayoutBoxRareData> rare_data_;
   scoped_refptr<const NGLayoutResult> cached_layout_result_;
 };