Bug 1594752, expose WindowGlobalParent's document title attribute to script, and fire a pagetitlechanged event on the frame/browser when it changes, r=nika

Differential Revision: https://phabricator.services.mozilla.com/D72561

dom/chrome-webidl/WindowGlobalActors.webidl

@@ -53,6 +53,7 @@ interface WindowGlobalParent : WindowContext {
   readonly attribute Principal documentPrincipal;
   readonly attribute Principal? contentBlockingAllowListPrincipal;
   readonly attribute URI? documentURI;
+  readonly attribute DOMString documentTitle;
 
   // Bit mask containing content blocking events that are recorded in
   // the document's content blocking log.

dom/ipc/WindowGlobalParent.cpp

@@ -6,6 +6,7 @@
 
 #include "mozilla/dom/WindowGlobalParent.h"
 
+#include "mozilla/AsyncEventDispatcher.h"
 #include "mozilla/ClearOnShutdown.h"
 #include "mozilla/ipc/InProcessParent.h"
 #include "mozilla/dom/BrowserBridgeParent.h"
@@ -279,7 +280,27 @@ IPCResult WindowGlobalParent::RecvUpdateDocumentPrincipal(
 }
 mozilla::ipc::IPCResult WindowGlobalParent::RecvUpdateDocumentTitle(
     const nsString& aTitle) {
+  if (mDocumentTitle == aTitle) {
+    return IPC_OK();
+  }
+
   mDocumentTitle = aTitle;
+
+  // Send a pagetitlechanged event only for changes to the title
+  // for top-level frames.
+  if (!BrowsingContext()->IsTop()) {
+    return IPC_OK();
+  }
+
+  Element* frameElement = BrowsingContext()->GetEmbedderElement();
+  if (!frameElement) {
+    return IPC_OK();
+  }
+
+  (new AsyncEventDispatcher(frameElement, NS_LITERAL_STRING("pagetitlechanged"),
+                            CanBubble::eYes, ChromeOnlyDispatch::eYes))
+      ->RunDOMEventWhenSafe();
+
   return IPC_OK();
 }
 

dom/ipc/WindowGlobalParent.h

@@ -120,7 +120,7 @@ class WindowGlobalParent final : public WindowContext,
   // The current URI which loaded in the document.
   nsIURI* GetDocumentURI() override { return mDocumentURI; }
 
-  const nsString& GetDocumentTitle() const { return mDocumentTitle; }
+  void GetDocumentTitle(nsAString& aTitle) const { aTitle = mDocumentTitle; }
 
   nsIPrincipal* GetContentBlockingAllowListPrincipal() const {
     return mDocContentBlockingAllowListPrincipal;

dom/media/mediasession/MediaSessionController.cpp

@@ -176,7 +176,7 @@ nsString MediaSessionController::GetDefaultTitle() const {
     }
     defaultTitle.AppendLiteral(" is playing media");
   } else {
-    defaultTitle = globalParent->GetDocumentTitle();
+    globalParent->GetDocumentTitle(defaultTitle);
   }
   return defaultTitle;
 }