Bug 1625930: Fire StyleSheetApplicableStateChanged event explicitly if the stylesheet is getten from the cache. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D81305

dom/base/Document.cpp

@@ -6587,23 +6587,7 @@ void Document::StyleSheetApplicableStateChanged(StyleSheet& aSheet) {
     }
   }
 
-  if (StyleSheetChangeEventsEnabled()) {
-    StyleSheetApplicableStateChangeEventInit init;
-    init.mBubbles = true;
-    init.mCancelable = true;
-    init.mStylesheet = &aSheet;
-    init.mApplicable = applicable;
-
-    RefPtr<StyleSheetApplicableStateChangeEvent> event =
-        StyleSheetApplicableStateChangeEvent::Constructor(
-            this, u"StyleSheetApplicableStateChanged"_ns, init);
-    event->SetTrusted(true);
-    event->SetTarget(this);
-    RefPtr<AsyncEventDispatcher> asyncDispatcher =
-        new AsyncEventDispatcher(this, event);
-    asyncDispatcher->mOnlyChromeDispatch = ChromeOnlyDispatch::eYes;
-    asyncDispatcher->PostDOMEvent();
-  }
+  PostStyleSheetApplicableStateChangeEvent(aSheet);
 
   if (!mSSApplicableStateNotificationPending) {
     MOZ_RELEASE_ASSERT(NS_IsMainThread());
@@ -6615,6 +6599,28 @@ void Document::StyleSheetApplicableStateChanged(StyleSheet& aSheet) {
   }
 }
 
+void Document::PostStyleSheetApplicableStateChangeEvent(StyleSheet& aSheet) {
+  if (!StyleSheetChangeEventsEnabled()) {
+    return;
+  }
+
+  StyleSheetApplicableStateChangeEventInit init;
+  init.mBubbles = true;
+  init.mCancelable = true;
+  init.mStylesheet = &aSheet;
+  init.mApplicable = aSheet.IsApplicable();
+
+  RefPtr<StyleSheetApplicableStateChangeEvent> event =
+      StyleSheetApplicableStateChangeEvent::Constructor(
+          this, u"StyleSheetApplicableStateChanged"_ns, init);
+  event->SetTrusted(true);
+  event->SetTarget(this);
+  RefPtr<AsyncEventDispatcher> asyncDispatcher =
+      new AsyncEventDispatcher(this, event);
+  asyncDispatcher->mOnlyChromeDispatch = ChromeOnlyDispatch::eYes;
+  asyncDispatcher->PostDOMEvent();
+}
+
 void Document::NotifyStyleSheetApplicableStateChanged() {
   mSSApplicableStateNotificationPending = false;
   nsCOMPtr<nsIObserverService> observerService =

dom/base/Document.h

@@ -1679,6 +1679,8 @@ class Document : public nsINode,
    */
   void StyleSheetApplicableStateChanged(StyleSheet&);
 
+  void PostStyleSheetApplicableStateChangeEvent(StyleSheet&);
+
   enum additionalSheetType {
     eAgentSheet,
     eUserSheet,

layout/style/SharedStyleSheetCache.cpp

@@ -317,6 +317,12 @@ void SharedStyleSheetCache::LoadCompletedInternal(
                  "should not get a forced unique inner during parsing");
       data->mSheet->SetComplete();
       data->ScheduleLoadEventIfNeeded();
+    } else if (data->mSheet->IsApplicable()) {
+      if (dom::Document* doc = data->mLoader->GetDocument()) {
+        // We post these events for devtools, even though the applicable state
+        // has not actually changed, to make the cache not observable.
+        doc->PostStyleSheetApplicableStateChangeEvent(*data->mSheet);
+      }
     }
 
     aDatasToNotify.AppendElement(data);