Let RenderTable reach table cells needing overflow recalc

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 3d10b9e684a3f0eea39b64db6f858918bcc23d1b..336558b72d651b4cf8209c3334bbe8f84bbaf55d 100644
--- a/Source/core/rendering/RenderTableSection.cpp
+++ b/Source/core/rendering/RenderTableSection.cpp
@@ -1129,6 +1129,30 @@ void RenderTableSection::computeOverflowFromCells(unsigned totalRows, unsigned n
     ASSERT(hasOverflowingCell == this->hasOverflowingCell());
 }
 
+bool RenderTableSection::recalcOverflowForCellsAfterStyleChange()
+{
+    unsigned totalRows = m_grid.size();
+    unsigned numEffCols = table()->numEffCols();
+    bool childrenOverflowChanged = false;
+
+    // Now that our height has been determined, add in overflow from cells.
+    for (unsigned r = 0; r < totalRows; r++) {
+        for (unsigned c = 0; c < numEffCols; c++) {
+            CellStruct& cs = cellAt(r, c);
+            RenderTableCell* cell = cs.primaryCell();
+            if (!cell || cs.inColSpan || !cell->needsOverflowRecalcAfterStyleChange())
+                continue;
+            if (cell->recalcOverflowAfterStyleChange())
+                childrenOverflowChanged = true;
+        }
+    }

[Julien - ping for review, 2014/11/22 02:35:04]

Recomputing the overflow is now O(columns*rows) :(

Overflow can only happen from table cells so they should just notify the section
that it needs to recompute the overflow.

[Xianzhu, 2014/11/24 17:23:00]

I think it's
  [O(columns*rows) of cost_of_testing_flag] + [O(N) of
cost_of_recomputing_overflow]
(N = number of cells needing recalc overflow).

If this looks not good, I can reduce the cost to
  [O(rows) + O(columns) of cost_of_testing_flag] + [O(N) of
cost_of_recomputing_overflow]
by also setting childNeedsRecalcOverflow flag on RenderTableRow and
RenderTableSection in markContainingBlocksForOverflowRecalc().

+
+    if (childrenOverflowChanged)
+        computeOverflowFromCells(totalRows, numEffCols);
+
+    return childrenOverflowChanged;
+}
+
 int RenderTableSection::calcBlockDirectionOuterBorder(BlockBorderSide side) const
 {
     unsigned totalCols = table()->numEffCols();