Adds clearer function to create rtc::Thread without Physical SocketServer
Moves logic of default SocketServer from MessageQueue to SocketServer

Review-Url: https://codereview.webrtc.org/1891293002
Cr-Commit-Position: refs/heads/master@{#12541}
diff --git a/webrtc/base/messagequeue_unittest.cc b/webrtc/base/messagequeue_unittest.cc
index 78024e0..31fb3bf 100644
--- a/webrtc/base/messagequeue_unittest.cc
+++ b/webrtc/base/messagequeue_unittest.cc
@@ -21,6 +21,7 @@
 
 class MessageQueueTest: public testing::Test, public MessageQueue {
  public:
+  MessageQueueTest() : MessageQueue(SocketServer::CreateDefault(), true) {}
   bool IsLocked_Worker() {
     if (!crit_.TryEnter()) {
       return true;
@@ -72,10 +73,11 @@
 
 TEST_F(MessageQueueTest,
        DelayedPostsWithIdenticalTimesAreProcessedInFifoOrder) {
-  MessageQueue q;
+  MessageQueue q(SocketServer::CreateDefault(), true);
   DelayedPostsWithIdenticalTimesAreProcessedInFifoOrder(&q);
+
   NullSocketServer nullss;
-  MessageQueue q_nullss(&nullss);
+  MessageQueue q_nullss(&nullss, true);
   DelayedPostsWithIdenticalTimesAreProcessedInFifoOrder(&q_nullss);
 }