Fixed some cctest flakiness on mac.

src/debug-agent.cc

Index: src/debug-agent.cc
diff --git a/src/debug-agent.cc b/src/debug-agent.cc
index 3dba53a435764f27505ee8c5862f61de59725ef8..9d5cace03ba1095dbcf27c90f9a271b75a913cc7 100644
--- a/src/debug-agent.cc
+++ b/src/debug-agent.cc
@@ -65,6 +65,7 @@ void DebuggerAgent::Run() {
   // Accept connections on the bound port.
   while (!terminate_) {
     bool ok = server_->Listen(1);
+    listening_->Signal();
     if (ok) {
       // Accept the new connection.
       Socket* client = server_->Accept();
@@ -93,6 +94,10 @@ void DebuggerAgent::Shutdown() {
 }
 
 
+void DebuggerAgent::WaitUntilListening() {
+  listening_->Wait();
+}
+
 void DebuggerAgent::CreateSession(Socket* client) {
   ScopedLock with(session_access_);