Fix google-explicit-constructor warnings in surfaceflinger.

* Add explicit keyword to conversion constructors,
  or use NOLINT for implicit converters.
Bug: 28341362
Test: build with WITH_TIDY=1

Change-Id: I94f511c3be31dc22022db6466ee9ed0c6be2bc8e
diff --git a/services/surfaceflinger/EventThread.h b/services/surfaceflinger/EventThread.h
index 34654fa..b635115 100644
--- a/services/surfaceflinger/EventThread.h
+++ b/services/surfaceflinger/EventThread.h
@@ -57,7 +57,7 @@
 class EventThread : public Thread, private VSyncSource::Callback {
     class Connection : public BnDisplayEventConnection {
     public:
-        Connection(const sp<EventThread>& eventThread);
+        explicit Connection(const sp<EventThread>& eventThread);
         status_t postEvent(const DisplayEventReceiver::Event& event);
 
         // count >= 1 : continuous event. count is the vsync rate