Bug 1618102 - Use BrowsingContext for Full screen API "is caller in focused tab?" check. r=farre

Differential Revision: https://phabricator.services.mozilla.com/D64288

--HG--
extra : moz-landing-system : lando

dom/base/Document.cpp

@@ -13429,28 +13429,45 @@ static bool IsInActiveTab(Document* aDoc) {
     return false;
   }
 
-  nsCOMPtr<nsIDocShellTreeItem> rootItem;
-  docshell->GetInProcessRootTreeItem(getter_AddRefs(rootItem));
-  if (!rootItem) {
-    return false;
-  }
-  nsCOMPtr<nsPIDOMWindowOuter> rootWin = rootItem->GetWindow();
-  if (!rootWin) {
-    return false;
-  }
-
-  nsIFocusManager* fm = nsFocusManager::GetFocusManager();
+  nsFocusManager* fm = nsFocusManager::GetFocusManager();
   if (!fm) {
     return false;
   }
 
-  nsCOMPtr<mozIDOMWindowProxy> activeWindow;
-  fm->GetActiveWindow(getter_AddRefs(activeWindow));
-  if (!activeWindow) {
+  if (XRE_IsParentProcess()) {
+    // Keep dom/tests/mochitest/chrome/test_MozDomFullscreen_event.xhtml happy
+    // by retaining the old code path for the parent process.
+
+    nsCOMPtr<nsIDocShellTreeItem> rootItem;
+    docshell->GetInProcessRootTreeItem(getter_AddRefs(rootItem));
+    if (!rootItem) {
+      return false;
+    }
+    nsCOMPtr<nsPIDOMWindowOuter> rootWin = rootItem->GetWindow();
+    if (!rootWin) {
+      return false;
+    }
+
+    nsCOMPtr<nsPIDOMWindowOuter> activeWindow;
+    activeWindow = fm->GetActiveWindow();
+    if (!activeWindow) {
+      return false;
+    }
+
+    return activeWindow == rootWin;
+  }
+
+  BrowsingContext* bc = aDoc->GetBrowsingContext();
+  if (!bc) {
     return false;
   }
 
-  return activeWindow == rootWin;
+  BrowsingContext* activeBrowsingContext = fm->GetActiveBrowsingContext();
+  if (!activeBrowsingContext) {
+    return false;
+  }
+
+  return activeBrowsingContext == bc->Top();
 }
 
 void Document::RemoteFrameFullscreenChanged(Element* aFrameElement) {