Fixing a couple cases that cause ProcessAllMessageQueues to hang.

webrtc/base/messagequeue.cc

Index: webrtc/base/messagequeue.cc
diff --git a/webrtc/base/messagequeue.cc b/webrtc/base/messagequeue.cc
index ebf98f58a34e3539a85bb4068bddadf8eab9c678..503d5aff966bde3354352173891fe93e91350ce6 100644
--- a/webrtc/base/messagequeue.cc
+++ b/webrtc/base/messagequeue.cc
@@ -126,17 +126,34 @@ void MessageQueueManager::ProcessAllMessageQueues() {
 }
 
 void MessageQueueManager::ProcessAllMessageQueuesInternal() {
-  // Post a delayed message at the current time and wait for it to be dispatched
-  // on all queues, which will ensure that all messages that came before it were
-  // also dispatched.
-  volatile int queues_not_done;
-  auto functor = [&queues_not_done] { AtomicOps::Decrement(&queues_not_done); };
-  FunctorMessageHandler<void, decltype(functor)> handler(functor);
+  // This works by posting a delayed message at the current time and waiting
+  // for it to be dispatched on all queues, which will ensure that all messages
+  // that came before it were also dispatched.
+  volatile int queues_not_done = 0;
+
+  // This class is used so that whether the posted message is processed, or the
+  // message queue is simply cleared, queues_not_done gets decremented.
+  class ScopedIncrement : public MessageData {
+   public:
+    ScopedIncrement(volatile int* value) : value_(value) {
+      AtomicOps::Increment(value_);
+    }
+    ~ScopedIncrement() override { AtomicOps::Decrement(value_); }
+
+   private:
+    volatile int* value_;
+  };
+
   {
     DebugNonReentrantCritScope cs(&crit_, &locked_);
-    queues_not_done = static_cast<int>(message_queues_.size());
     for (MessageQueue* queue : message_queues_) {
-      queue->PostDelayed(RTC_FROM_HERE, 0, &handler);
+      if (queue->IsQuitting()) {
+        // If the queue is quitting, it's done processing messages so it can
+        // be ignored. If we tried to post a message to it, it would be dropped.
+        continue;
+      }
+      queue->PostDelayed(RTC_FROM_HERE, 0, nullptr, MQID_DISPOSE,
+                         new ScopedIncrement(&queues_not_done));
     }
   }
   // Note: One of the message queues may have been on this thread, which is why