rework client using async api

autotest/client_timeout_autotest/main.cc

@@ -0,0 +1,11 @@
+#include "gtest/gtest.h"
+
+#include "webcc/logger.h"
+
+int main(int argc, char* argv[]) {
+  // Set webcc::LOG_CONSOLE to enable logging.
+  WEBCC_LOG_INIT("", 0);
+
+  ::testing::InitGoogleTest(&argc, argv);
+  return RUN_ALL_TESTS();
+}