Fix cpplint runtime/explicit issues

Change-Id: I352ba0b427f1ff9b22887693952b180eae0839ba
diff --git a/runtime/jdwp/jdwp_adb.cc b/runtime/jdwp/jdwp_adb.cc
index 9652f60..9b9fe4c 100644
--- a/runtime/jdwp/jdwp_adb.cc
+++ b/runtime/jdwp/jdwp_adb.cc
@@ -54,7 +54,7 @@
 
 struct JdwpAdbState : public JdwpNetStateBase {
  public:
-  JdwpAdbState(JdwpState* state) : JdwpNetStateBase(state) {
+  explicit JdwpAdbState(JdwpState* state) : JdwpNetStateBase(state) {
     control_sock_ = -1;
     shutting_down_ = false;
 
diff --git a/runtime/jdwp/jdwp_priv.h b/runtime/jdwp/jdwp_priv.h
index ab89339..557632c 100644
--- a/runtime/jdwp/jdwp_priv.h
+++ b/runtime/jdwp/jdwp_priv.h
@@ -53,7 +53,7 @@
  */
 class JdwpNetStateBase {
  public:
-  JdwpNetStateBase(JdwpState*);
+  explicit JdwpNetStateBase(JdwpState*);
   virtual ~JdwpNetStateBase();
 
   virtual bool Accept() = 0;
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;
   }