[Slimming paint] [New Multicolumn] Repaint column rules when they change.

Source/core/rendering/style/RenderStyle.h

Index: Source/core/rendering/style/RenderStyle.h
diff --git a/Source/core/rendering/style/RenderStyle.h b/Source/core/rendering/style/RenderStyle.h
index 342b9dc636ea60ce1ceb4a9424a43faa86a2c309..20ccf9aefe14ec39bdb46c6e565a15c4580c5081 100644
--- a/Source/core/rendering/style/RenderStyle.h
+++ b/Source/core/rendering/style/RenderStyle.h
@@ -809,6 +809,7 @@ public:
     EBorderStyle columnRuleStyle() const { return rareNonInheritedData->m_multiCol->m_rule.style(); }
     unsigned short columnRuleWidth() const { return rareNonInheritedData->m_multiCol->ruleWidth(); }
     bool columnRuleIsTransparent() const { return rareNonInheritedData->m_multiCol->m_rule.isTransparent(); }
+    bool columnRuleEquivalent(const RenderStyle* otherStyle) const;
     ColumnSpan columnSpan() const { return static_cast<ColumnSpan>(rareNonInheritedData->m_multiCol->m_columnSpan); }
     EPageBreak columnBreakBefore() const { return static_cast<EPageBreak>(rareNonInheritedData->m_multiCol->m_breakBefore); }
     EPageBreak columnBreakInside() const { return static_cast<EPageBreak>(rareNonInheritedData->m_multiCol->m_breakInside); }