Bug 1808691 - Handle re-entrance in SignalImpendingShutdownToContentJS. r=smaug

Differential Revision: https://phabricator.services.mozilla.com/D166051

dom/ipc/ContentParent.cpp

@@ -3723,10 +3723,12 @@ class RequestContentJSInterruptRunnable final : public Runnable {
 };
 
 void ContentParent::SignalImpendingShutdownToContentJS() {
-  if (!AppShutdown::IsInOrBeyond(ShutdownPhase::AppShutdown)) {
+  if (!mIsSignaledImpendingShutdown &&
+      !AppShutdown::IsInOrBeyond(ShutdownPhase::AppShutdown)) {
     MaybeLogBlockShutdownDiagnostics(
         this, "BlockShutdown: NotifyImpendingShutdown.", __FILE__, __LINE__);
     NotifyImpendingShutdown();
+    mIsSignaledImpendingShutdown = true;
     if (mHangMonitorActor &&
         StaticPrefs::dom_abort_script_on_child_shutdown()) {
       MaybeLogBlockShutdownDiagnostics(

dom/ipc/ContentParent.h

@@ -1660,6 +1660,7 @@ class ContentParent final : public PContentParent,
   static uint32_t sPageLoadEventCounter;
   static Maybe<TimeStamp> sLastContentProcessLaunch;
 
+  bool mIsSignaledImpendingShutdown = false;
   bool mIsNotifiedShutdownSuccess = false;
 };