Fix cpplint runtime/explicit issues

Change-Id: I352ba0b427f1ff9b22887693952b180eae0839ba
diff --git a/runtime/jdwp/jdwp_socket.cc b/runtime/jdwp/jdwp_socket.cc
index 08b4859..87706a4 100644
--- a/runtime/jdwp/jdwp_socket.cc
+++ b/runtime/jdwp/jdwp_socket.cc
@@ -46,7 +46,7 @@
   uint16_t listenPort;
   int     listenSock;         /* listen for connection from debugger */
 
-  JdwpSocketState(JdwpState* state) : JdwpNetStateBase(state) {
+  explicit JdwpSocketState(JdwpState* state) : JdwpNetStateBase(state) {
     listenPort  = 0;
     listenSock  = -1;
   }