Add a first pass of a class descendant invalidator, and a containing RuleSetAnalyzer

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 0e4ca1c203c9561b7e3962dbf19acdfb022a937e..5b76d8d5a398f9d856f0f385ad233ceb69e4439c 100644
--- a/Source/core/rendering/style/RenderStyle.h
+++ b/Source/core/rendering/style/RenderStyle.h
@@ -1716,6 +1716,10 @@ public:
     static const FilterOperations& initialFilter() { DEFINE_STATIC_LOCAL(FilterOperations, ops, ()); return ops; }
     static blink::WebBlendMode initialBlendMode() { return blink::WebBlendModeNormal; }
     static EIsolation initialIsolation() { return IsolationAuto; }
+
+    Color backgroundColor() const { return m_background->color(); }
+
+
 private:
     void setVisitedLinkColor(const Color&);
     void setVisitedLinkBackgroundColor(const Color& v) { SET_VAR(rareNonInheritedData, m_visitedLinkBackgroundColor, v); }
@@ -1761,7 +1765,6 @@ private:
     Color borderRightColor() const { return surround->border.right().color(); }
     Color borderTopColor() const { return surround->border.top().color(); }
     Color borderBottomColor() const { return surround->border.bottom().color(); }
-    Color backgroundColor() const { return m_background->color(); }
     Color color() const;
     Color columnRuleColor() const { return rareNonInheritedData->m_multiCol->m_rule.color(); }
     Color outlineColor() const { return m_background->outline().color(); }