Optimize number of rowspan cells required to distribute their height in rows.

Source/core/rendering/RenderTableSection.cpp

Index: Source/core/rendering/RenderTableSection.cpp
diff --git a/Source/core/rendering/RenderTableSection.cpp b/Source/core/rendering/RenderTableSection.cpp
index da4b53a56e5c1fb5c6908e7bd47bd46eca864cab..b49f47f6987963472b955849aa78f06dab026038 100644
--- a/Source/core/rendering/RenderTableSection.cpp
+++ b/Source/core/rendering/RenderTableSection.cpp
@@ -528,6 +528,9 @@ int RenderTableSection::calcRowLogicalHeight()
         m_rowPos[0] = 0;
 
     SpanningRenderTableCells rowSpanCells;
+#ifndef NDEBUG
+    HashSet<const RenderTableCell*> uniqueCells;
+#endif
 
     for (unsigned r = 0; r < m_grid.size(); r++) {
         m_grid[r].baseline = 0;
@@ -538,6 +541,7 @@ int RenderTableSection::calcRowLogicalHeight()
 
         Row& row = m_grid[r].row;
         unsigned totalCols = row.size();
+        RenderTableCell* lastRowSpanCell = 0;
 
         for (unsigned c = 0; c < totalCols; c++) {
             CellStruct& current = cellAt(r, c);
@@ -549,8 +553,14 @@ int RenderTableSection::calcRowLogicalHeight()
                 if (RuntimeEnabledFeatures::rowSpanLogicalHeightSpreadingEnabled()) {
                     if (cell->rowSpan() > 1) {
                         // For row spanning cells, we only handle them for the first row they span. This ensures we take their baseline into account.
-                        if (cell->rowIndex() == r) {
+                        if (lastRowSpanCell != cell && cell->rowIndex() == r) {
+#ifndef NDEBUG
+                            ASSERT(!uniqueCells.contains(cell));
+                            uniqueCells.add(cell);
+#endif
+
                             rowSpanCells.append(cell);
+                            lastRowSpanCell = cell;
 
                             // Find out the baseline. The baseline is set on the first row in a rowSpan.
                             updateBaselineForCell(cell, r, baselineDescent);