Move widow-avoiding code from RenderBlock down to RenderBlockFlow.

Source/core/rendering/RenderBlockFlow.h

Index: Source/core/rendering/RenderBlockFlow.h
diff --git a/Source/core/rendering/RenderBlockFlow.h b/Source/core/rendering/RenderBlockFlow.h
index 71be858e4a55902c2e011c35bc1d9da3170707af..7b2d9f6413a6f4dc029507bccd3f336bb16de88d 100644
--- a/Source/core/rendering/RenderBlockFlow.h
+++ b/Source/core/rendering/RenderBlockFlow.h
@@ -314,6 +314,14 @@ private:
     bool shouldRelayoutForPagination(LayoutUnit& pageLogicalHeight, LayoutUnit layoutOverflowLogicalBottom) const;
     void setColumnCountAndHeight(unsigned count, LayoutUnit pageLogicalHeight);
 
+    bool shouldBreakAtLineToAvoidWidow() const { return m_rareData && m_rareData->m_lineBreakToAvoidWidow >= 0; }
+    void clearShouldBreakAtLineToAvoidWidow() const;
+    int lineBreakToAvoidWidow() const { return m_rareData ? m_rareData->m_lineBreakToAvoidWidow : -1; }
+    void setBreakAtLineToAvoidWidow(int);
+    void clearDidBreakAtLineToAvoidWidow();
+    void setDidBreakAtLineToAvoidWidow();
+    bool didBreakAtLineToAvoidWidow() const { return m_rareData && m_rareData->m_didBreakAtLineToAvoidWidow; }
+
 public:
     struct FloatWithRect {
         FloatWithRect(RenderBox* f)
@@ -363,6 +371,8 @@ public:
             : m_margins(positiveMarginBeforeDefault(block), negativeMarginBeforeDefault(block), positiveMarginAfterDefault(block), negativeMarginAfterDefault(block))
             , m_paginationStrut(0)
             , m_multiColumnFlowThread(0)
+            , m_lineBreakToAvoidWidow(-1)
+            , m_didBreakAtLineToAvoidWidow(false)
             , m_discardMarginBefore(false)
             , m_discardMarginAfter(false)
         {
@@ -390,6 +400,8 @@ public:
 
         RenderMultiColumnFlowThread* m_multiColumnFlowThread;
 
+        int m_lineBreakToAvoidWidow;
+        bool m_didBreakAtLineToAvoidWidow : 1;
         bool m_discardMarginBefore : 1;
         bool m_discardMarginAfter : 1;
     };