Fix deadlock when terminating debugger session.

BUG=
TEST=

Review URL: https://chromiumcodereview.appspot.com/10479009

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@11705 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

src/debug-agent.cc

@@ -157,7 +157,9 @@ void DebuggerAgent::OnSessionClosed(DebuggerAgentSession* session) {
   ScopedLock with(session_access_);
   ASSERT(session == session_);
   if (session == session_) {
-    CloseSession();
+    session_->Shutdown();
+    delete session_;
+    session_ = NULL;
   }
 }