Let collapsed border drawings be cacheable

Source/core/layout/LayoutTableSection.cpp

Index: Source/core/layout/LayoutTableSection.cpp
diff --git a/Source/core/layout/LayoutTableSection.cpp b/Source/core/layout/LayoutTableSection.cpp
index 13715dbd10623afcc0edecbfdecc50b7cad9f90b..f8e4c0b3927abd5e0178c2ee1c8cbc06a382e505 100644
--- a/Source/core/layout/LayoutTableSection.cpp
+++ b/Source/core/layout/LayoutTableSection.cpp
@@ -1602,14 +1602,19 @@ void LayoutTableSection::removeCachedCollapsedBorders(const LayoutTableCell* cel
         m_cellsCollapsedBorders.remove(std::make_pair(cell, side));
 }
 
-void LayoutTableSection::setCachedCollapsedBorder(const LayoutTableCell* cell, CollapsedBorderSide side, const CollapsedBorderValue& border)
+bool LayoutTableSection::setCachedCollapsedBorder(const LayoutTableCell* cell, CollapsedBorderSide side, const CollapsedBorderValue& border)
 {
     ASSERT(table()->collapseBorders());
     CellsCollapsedBordersMap::iterator it = m_cellsCollapsedBorders.find(std::make_pair(cell, side));
-    if (it == m_cellsCollapsedBorders.end())
+    if (it == m_cellsCollapsedBorders.end()) {
         m_cellsCollapsedBorders.add(std::make_pair(cell, side), border);
-    else
+        return true;
+    }
+    if (!it->value.equals(border)) {
         it->value = border;
+        return true;
+    }
+    return false;
 }
 
 const CollapsedBorderValue& LayoutTableSection::cachedCollapsedBorder(const LayoutTableCell* cell, CollapsedBorderSide side) const