Bug 1341648 - stylo: Include content rules from HTMLTableCellElement::WalkContentStyleRules ; r=bz

This also removes the TABLE_ATTRS_DIRTY optimization. Constructing nsMappedAttributes isn't really expensive and we do it all the time anyway.

MozReview-Commit-ID: 2krt1nFUzgl

dom/html/HTMLTableCellElement.h

@@ -148,6 +148,8 @@ public:
   virtual nsMapRuleToAttributesFunc GetAttributeMappingFunction() const override;
   NS_IMETHOD WalkContentStyleRules(nsRuleWalker* aRuleWalker) override;
   NS_IMETHOD_(bool) IsAttributeMapped(const nsIAtom* aAttribute) const override;
+  // Get mapped attributes of ancestor table, if any
+  nsMappedAttributes* GetMappedAttributesInheritedFromTable() const;
 
   virtual nsresult Clone(mozilla::dom::NodeInfo *aNodeInfo, nsINode **aResult) const override;