Bug 1475351: Properly clear associated ShadowRoot from StyleSheet objects. r=smaug

Just like we do from the document's destructor.

MozReview-Commit-ID: DygmZ0EI9es

dom/base/DocumentOrShadowRoot.cpp

@@ -25,6 +25,13 @@ DocumentOrShadowRoot::DocumentOrShadowRoot(nsIDocument& aDoc)
   , mKind(Kind::Document)
 {}
 
+DocumentOrShadowRoot::~DocumentOrShadowRoot()
+{
+  for (StyleSheet* sheet : mStyleSheets) {
+    sheet->ClearAssociatedDocumentOrShadowRoot();
+  }
+}
+
 StyleSheetList&
 DocumentOrShadowRoot::EnsureDOMStyleSheets()
 {

dom/base/DocumentOrShadowRoot.h

@@ -100,7 +100,7 @@ public:
   already_AddRefed<nsContentList>
   GetElementsByClassName(const nsAString& aClasses);
 
-  ~DocumentOrShadowRoot() = default;
+  ~DocumentOrShadowRoot();
 
   Element* GetPointerLockElement();
   Element* GetFullscreenElement();

dom/base/nsDocument.cpp

@@ -1684,15 +1684,12 @@ nsDocument::~nsDocument()
   mFirstChild = nullptr;
   mCachedRootElement = nullptr;
 
-  // Let the stylesheets know we're going away
-  for (StyleSheet* sheet : mStyleSheets) {
-    sheet->ClearAssociatedDocumentOrShadowRoot();
-  }
   for (auto& sheets : mAdditionalSheets) {
     for (StyleSheet* sheet : sheets) {
       sheet->ClearAssociatedDocumentOrShadowRoot();
     }
   }
+
   if (mAttrStyleSheet) {
     mAttrStyleSheet->SetOwningDocument(nullptr);
   }