[TablesNG] TableConstraintSpaceData memory optimization

Make all rows share the same TableConstraintSpaceData by
replacing it if we are reusing the fragment.

Bug: 958381
Change-Id: I7647d69d930218f1dfaac2cefdd8a49ba936ceaf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2511431
Commit-Queue: Aleks Totic <atotic@chromium.org>
Reviewed-by: Ian Kilpatrick <ikilpatrick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823562}

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

@@ -3498,6 +3498,14 @@ scoped_refptr<const NGLayoutResult> LayoutBox::CachedLayoutResult(
   // not clear the child dirty bits.
   ClearNeedsLayout();
 
+  // Optimization: TableConstraintSpaceData can be large, and it is shared
+  // between all the rows in a table. Make constraint space table data for
+  // reused row fragment be identical to the one used by other row fragments.
+  if (IsTableRow() && IsLayoutNGMixin()) {
+    const_cast<NGConstraintSpace&>(old_space).ReplaceTableConstraintSpaceData(
+        *new_space.TableData());
+  }
+
   // OOF-positioned nodes have to two-tier cache. The additional cache check
   // runs before the OOF-positioned sizing, and positioning calculations.
   //

third_party/blink/renderer/core/layout/ng/ng_constraint_space.h

@@ -685,6 +685,12 @@ class CORE_EXPORT NGConstraintSpace final {
     return true;
   }
 
+  void ReplaceTableConstraintSpaceData(
+      const NGTableConstraintSpaceData& table_data) {
+    DCHECK(HasRareData());
+    rare_data_->ReplaceTableConstraintSpaceData(table_data);
+  }
+
   String ToString() const;
 
  private:
@@ -998,6 +1004,14 @@ class CORE_EXPORT NGConstraintSpace final {
       EnsureTableSectionData()->section_index = section_index;
     }
 
+    void ReplaceTableConstraintSpaceData(
+        const NGTableConstraintSpaceData& table_data) {
+      DCHECK_EQ(data_union_type, kTableRowData);
+      DCHECK(table_data.IsTableSpecificDataEqual(
+          *(EnsureTableRowData()->table_data)));
+      EnsureTableRowData()->table_data = &table_data;
+    }
+
     const NGTableConstraintSpaceData* TableData() {
       if (data_union_type == kTableRowData)
         return EnsureTableRowData()->table_data.get();