Fix google-explicit-constructor warnings in binder.

* Add explicit keyword to conversion constructors.
Bug: 28341362
Test: build with WITH_TIDY=1

Change-Id: I166ab302b3e842cb6d27de89e85767c459f7d826
diff --git a/include/binder/IInterface.h b/include/binder/IInterface.h
index 48c8b3b..be72d44 100644
--- a/include/binder/IInterface.h
+++ b/include/binder/IInterface.h
@@ -63,7 +63,7 @@
 class BpInterface : public INTERFACE, public BpRefBase
 {
 public:
-                                BpInterface(const sp<IBinder>& remote);
+    explicit                    BpInterface(const sp<IBinder>& remote);
 
 protected:
     virtual IBinder*            onAsBinder();