1 files changed, 22 insertions, 1 deletions
diff --git a/dom/base/StyleSheetList.cpp b/dom/base/StyleSheetList.cpp
index 7274b5ea5..42db3179d 100644
--- a/dom/base/StyleSheetList.cpp
+++ b/dom/base/StyleSheetList.cpp
@@ -8,6 +8,7 @@
 
 #include "mozilla/CSSStyleSheet.h"
 #include "mozilla/dom/StyleSheetListBinding.h"
+#include "nsStubDocumentObserver.h"
 
 namespace mozilla {
 namespace dom {
@@ -17,7 +18,8 @@ NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(StyleSheetList)
 NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(StyleSheetList)
   NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY
   NS_INTERFACE_MAP_ENTRY(nsIDOMStyleSheetList)
-  NS_INTERFACE_MAP_ENTRY(nsISupports)
+  NS_INTERFACE_MAP_ENTRY(nsIMutationObserver)
+  NS_INTERFACE_MAP_ENTRY_AMBIGUOUS(nsISupports, nsIDOMStyleSheetList)
 NS_INTERFACE_MAP_END
 
 NS_IMPL_CYCLE_COLLECTING_ADDREF(StyleSheetList)
@@ -43,5 +45,24 @@ StyleSheetList::SlowItem(uint32_t aIndex, nsIDOMStyleSheet** aItem)
   return NS_OK;
 }
 
+void
+StyleSheetList::NodeWillBeDestroyed(const nsINode* aNode)
+{
+  mStyleScope = nullptr;
+}
+
+StyleSheetList::StyleSheetList(StyleScope& aScope)
+  : mStyleScope(&aScope)
+{
+  mStyleScope->AsNode().AddMutationObserver(this);
+}
+
+StyleSheetList::~StyleSheetList()
+{
+  if (mStyleScope) {
+    mStyleScope->AsNode().RemoveMutationObserver(this);
+  }
+}
+
 } // namespace dom
 } // namespace mozilla