Reland: Lazily initialize MessageLoop for faster thread startup

net/test/embedded_test_server/embedded_test_server.cc

Index: net/test/embedded_test_server/embedded_test_server.cc
diff --git a/net/test/embedded_test_server/embedded_test_server.cc b/net/test/embedded_test_server/embedded_test_server.cc
index ac7d3bc14ac74f56b31f3ab83f5c7511f8cf6fb9..e747c9483bd4ac2190b56badcc9b4b6303b96ae7 100644
--- a/net/test/embedded_test_server/embedded_test_server.cc
+++ b/net/test/embedded_test_server/embedded_test_server.cc
@@ -190,6 +190,7 @@ void EmbeddedTestServer::StartThread() {
   thread_options.message_loop_type = base::MessageLoop::TYPE_IO;
   io_thread_.reset(new base::Thread("EmbeddedTestServer io thread"));
   CHECK(io_thread_->StartWithOptions(thread_options));
+  CHECK(io_thread_->WaitUntilThreadStarted());
 }
 
 void EmbeddedTestServer::InitializeOnIOThread() {