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/Layer.h b/services/surfaceflinger/Layer.h
index ba7184f..55e3b54 100644
--- a/services/surfaceflinger/Layer.h
+++ b/services/surfaceflinger/Layer.h
@@ -456,7 +456,7 @@
     class SyncPoint
     {
     public:
-        SyncPoint(uint64_t frameNumber) : mFrameNumber(frameNumber),
+        explicit SyncPoint(uint64_t frameNumber) : mFrameNumber(frameNumber),
                 mFrameIsAvailable(false), mTransactionIsApplied(false) {}
 
         uint64_t getFrameNumber() const {