Bug 1454251: followup: add a missing include to fix fuzzing builds on a CLOSED TREE. r=me

MozReview-Commit-ID: IpL9tgiufpt

dom/base/Attr.h

@@ -13,6 +13,8 @@
 
 #include "mozilla/Attributes.h"
 #include "nsIAttribute.h"
+#include "nsIContent.h" // For NS_IMPL_FROMNODE_HELPER, though looks like it
+                        // should live in nsINode.h?
 #include "nsIDOMNode.h"
 #include "nsIDOMNodeList.h"
 #include "nsString.h"