Bug 1513681 - part1 : dispatch 'GloballyAutoplayBlocked' event when site is blocked r=cpearce,smaug

This event is used to notify tab that this site is blocked and we should show the blocking icon for it. Patch2 will handle following details.

Differential Revision: https://phabricator.services.mozilla.com/D14794

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

dom/base/Document.cpp

@@ -11738,6 +11738,20 @@ void Document::NotifyUserGestureActivation() {
   }
 }
 
+void Document::MaybeNotifyAutoplayBlocked() {
+  Document* topLevelDoc = GetTopLevelContentDocument();
+  if (!topLevelDoc) {
+    return;
+  }
+
+  // This event is used to notify front-end side that we've blocked autoplay,
+  // so front-end side should show blocking icon as well.
+  RefPtr<AsyncEventDispatcher> asyncDispatcher = new AsyncEventDispatcher(
+      topLevelDoc, NS_LITERAL_STRING("GloballyAutoplayBlocked"),
+      CanBubble::eYes, ChromeOnlyDispatch::eYes);
+  asyncDispatcher->PostDOMEvent();
+}
+
 void Document::SetDocTreeHadAudibleMedia() {
   Document* topLevelDoc = GetTopLevelContentDocument();
   if (!topLevelDoc) {

dom/base/Document.h

@@ -3485,6 +3485,10 @@ class Document : public nsINode,
 
   void ReportShadowDOMUsage();
 
+  // When the doc is blocked permanantly, we would dispatch event to notify
+  // front-end side to show blocking icon.
+  void MaybeNotifyAutoplayBlocked();
+
   // Sets flags for media autoplay telemetry.
   void SetDocTreeHadAudibleMedia();
   void SetDocTreeHadPlayRevoked();

dom/html/HTMLMediaElement.cpp

@@ -3697,6 +3697,7 @@ void HTMLMediaElement::DispatchEventsWhenPlayWasNotAllowed() {
       ChromeOnlyDispatch::eYes);
   asyncDispatcher->PostDOMEvent();
 #endif
+  OwnerDoc()->MaybeNotifyAutoplayBlocked();
 }
 
 void HTMLMediaElement::PlayInternal(bool aHandlingUserInput) {