Bug 1449522 - Cleanup some parent walks in StyleSheet code. r=nordzilla

Differential Revision: https://phabricator.services.mozilla.com/D71410

layout/style/StyleSheet.cpp

@@ -159,28 +159,26 @@ Document* StyleSheet::GetAssociatedDocument() const {
 
 dom::DocumentOrShadowRoot* StyleSheet::GetAssociatedDocumentOrShadowRoot()
     const {
-  for (const auto* sheet = this; sheet; sheet = sheet->mParentSheet) {
-    if (sheet->mDocumentOrShadowRoot) {
-      return sheet->mDocumentOrShadowRoot;
-    }
-    if (sheet->IsConstructed()) {
-      return sheet->mConstructorDocument;
+  const StyleSheet& outer = OutermostSheet();
+  if (outer.mDocumentOrShadowRoot) {
+    return outer.mDocumentOrShadowRoot;
   }
+  if (outer.IsConstructed()) {
+    return outer.mConstructorDocument;
   }
   return nullptr;
 }
 
 Document* StyleSheet::GetKeptAliveByDocument() const {
-  for (const auto* sheet = this; sheet; sheet = sheet->mParentSheet) {
-    if (sheet->mDocumentOrShadowRoot) {
-      return sheet->mDocumentOrShadowRoot->AsNode().GetComposedDoc();
+  const StyleSheet& outer = OutermostSheet();
+  if (outer.mDocumentOrShadowRoot) {
+    return outer.mDocumentOrShadowRoot->AsNode().GetComposedDoc();
   }
-    if (sheet->IsConstructed()) {
-      for (DocumentOrShadowRoot* adopter : sheet->mAdopters) {
-        MOZ_ASSERT(adopter->AsNode().OwnerDoc() == sheet->mConstructorDocument);
+  if (outer.IsConstructed()) {
+    for (DocumentOrShadowRoot* adopter : outer.mAdopters) {
+      MOZ_ASSERT(adopter->AsNode().OwnerDoc() == outer.mConstructorDocument);
       if (adopter->AsNode().IsInComposedDoc()) {
-          return sheet->mConstructorDocument.get();
-        }
+        return outer.mConstructorDocument.get();
       }
     }
   }
@@ -306,16 +304,15 @@ void StyleSheet::ApplicableStateChanged(bool aApplicable) {
     }
   };
 
-  for (const auto* sheet = this; sheet; sheet = sheet->mParentSheet) {
-    if (sheet->mDocumentOrShadowRoot) {
-      Notify(*sheet->mDocumentOrShadowRoot);
+  const StyleSheet& sheet = OutermostSheet();
+  if (sheet.mDocumentOrShadowRoot) {
+    Notify(*sheet.mDocumentOrShadowRoot);
   }
 
-    for (DocumentOrShadowRoot* adopter : sheet->mAdopters) {
+  for (DocumentOrShadowRoot* adopter : sheet.mAdopters) {
     MOZ_ASSERT(adopter, "adopters should never be null");
     Notify(*adopter);
   }
-  }
 }
 
 void StyleSheet::SetDisabled(bool aDisabled) {

layout/style/StyleSheet.h

@@ -394,12 +394,7 @@ class StyleSheet final : public nsICSSLoaderObserver, public nsWrapperCache {
   // True if any of this sheet's ancestors were created through the
   // Constructable StyleSheets API
   bool SelfOrAncestorIsConstructed() const {
-    for (auto* sheet = this; sheet; sheet = sheet->mParentSheet) {
-      if (sheet->IsConstructed()) {
-        return true;
-      }
-    }
-    return false;
+    return OutermostSheet().IsConstructed();
   }
 
   // Ture if the sheet's constructor document matches the given document
@@ -473,6 +468,18 @@ class StyleSheet final : public nsICSSLoaderObserver, public nsWrapperCache {
     mState |= State::ModifiedRules | State::ModifiedRulesForDevtools;
   }
 
+  const StyleSheet& OutermostSheet() const {
+    auto* current = this;
+    while (current->mParentSheet) {
+      MOZ_ASSERT(!current->mDocumentOrShadowRoot,
+                 "Shouldn't be set on child sheets");
+      MOZ_ASSERT(!current->mConstructorDocument,
+                 "Shouldn't be set on child sheets");
+      current = current->mParentSheet;
+    }
+    return *current;
+  }
+
   StyleSheetInfo& Inner() {
     MOZ_ASSERT(mInner);
     return *mInner;