[DOM events] Re-apply clear event listener.

This was lost somewhere. commit 0fad293135

dom/events/EventListenerManager.cpp

@@ -702,6 +702,8 @@ EventListenerManager::SetEventHandlerInternal(
                         const TypedEventHandler& aTypedHandler,
                         bool aPermitUntrustedEvents)
 {
+  auto removeEventHandler = MakeScopeExit([&] { RemoveEventHandler(aName, EmptyString()); });
+  
   MOZ_ASSERT(aName || !aTypeString.IsEmpty());
 
   EventMessage eventMessage = nsContentUtils::GetEventMessage(aName);
@@ -737,6 +739,8 @@ EventListenerManager::SetEventHandlerInternal(
     }
   }
 
+  removeEventHandler.release();
+  
   // Set flag to indicate possible need for compilation later
   listener->mHandlerIsString = !aTypedHandler.HasEventHandler();
   if (aPermitUntrustedEvents) {
@@ -753,8 +757,6 @@ EventListenerManager::SetEventHandler(nsIAtom* aName,
                                       bool aPermitUntrustedEvents,
                                       Element* aElement)
 {
-  auto removeEventHandler = MakeScopeExit([&] { RemoveEventHandler(aName, EmptyString()); });
-
   nsCOMPtr<nsIDocument> doc;
   nsCOMPtr<nsIScriptGlobalObject> global =
     GetScriptGlobalAndDocument(getter_AddRefs(doc));
@@ -829,8 +831,6 @@ EventListenerManager::SetEventHandler(nsIAtom* aName,
   NS_ENSURE_TRUE(context, NS_ERROR_FAILURE);
   NS_ENSURE_STATE(global->GetGlobalJSObject());
 
-  removeEventHandler.release();
-
   Listener* listener = SetEventHandlerInternal(aName,
                                                EmptyString(),
                                                TypedEventHandler(),

xpcom/threads/TimerThread.cpp

@@ -623,7 +623,6 @@ TimerThread::AddTimerInternal(nsTimerImpl* aTimer)
   return insertSlot - mTimers.Elements();
 }
 
-// Note: this function must be called from within a lock.
 bool
 TimerThread::RemoveTimerInternal(nsTimerImpl* aTimer)
 {
@@ -691,17 +690,12 @@ TimerThread::PostTimerEvent(already_AddRefed<nsTimerImpl> aTimerRef)
     // at the TimerThread we'll deadlock.
     MonitorAutoUnlock unlock(mMonitor);
     rv = target->Dispatch(event, NS_DISPATCH_NORMAL);
-    if (NS_FAILED(rv)) {
-      timer = event->ForgetTimer();
-      // We do this to avoid possible deadlock by taking the two locks in a
-      // different order than is used in RemoveTimer(). RemoveTimer() has
-      // aTimer->mMutex first. We use timer.get() to keep static analysis
-      // happy.
-      MutexAutoLock lock1(timer.get()->mMutex);
-      MonitorAutoLock lock2(mMonitor);
-      RemoveTimerInternal(timer.get());
-      return timer.forget();
-    }
+  }
+
+  if (NS_FAILED(rv)) {
+    timer = event->ForgetTimer();
+    RemoveTimerInternal(timer);
+    return timer.forget();
   }
 
   return nullptr;

xpcom/threads/TimerThread.h

@@ -69,10 +69,6 @@ private:
   already_AddRefed<nsTimerImpl> PostTimerEvent(already_AddRefed<nsTimerImpl> aTimerRef);
 
   nsCOMPtr<nsIThread> mThread;
-  // Lock ordering requirements:
-  // (optional) ThreadWrapper::sMutex ->
-  // (optional) nsTimerImpl::mMutex   ->
-  // TimerThread::mMonitor
   Monitor mMonitor;
 
   bool mShutdown;

xpcom/threads/nsTimerImpl.cpp

@@ -441,8 +441,6 @@ nsTimerImpl::Fire(int32_t aGeneration)
     // Don't fire callbacks or fiddle with refcounts when the mutex is locked.
     // If some other thread Cancels/Inits after this, they're just too late.
     if (aGeneration != mGeneration) {
-      // This timer got rescheduled or cancelled before we fired, so ignore this
-      // firing
       return;
     }
 

xpcom/threads/nsTimerImpl.h

@@ -166,10 +166,7 @@ public:
   int32_t               mGeneration;
 
   uint32_t              mDelay;
-  // Never updated while in the TimerThread's timer list. Only updated
-  // before adding to that list or during nsTimerImpl::Fire(), when it has
-  // been removed from the TimerThread's list. TimerThread can safely access
-  // mTimeout of any timer in the list.
+  // Updated only after this timer has been removed from the timer thread.
   TimeStamp             mTimeout;
 
 #ifdef MOZ_TASK_TRACER