Bug 591737 - Implement toggling open details by mouse click. r=bz

dom/html/HTMLSummaryElement.h

@@ -11,6 +11,7 @@
 
 namespace mozilla {
 namespace dom {
+class HTMLDetailsElement;
 
 // HTMLSummaryElement implements the <summary> tag, which is used as a summary
 // or legend of the <details> tag. Please see the spec for more information.
@@ -30,6 +31,8 @@ public:
 
   nsresult Clone(NodeInfo* aNodeInfo, nsINode** aResult) const override;
 
+  nsresult PostHandleEvent(EventChainPostVisitor& aVisitor) override;
+
   // Return true if this is the first summary element child of a details or the
   // default summary element generated by DetailsFrame.
   bool IsMainSummary() const;