Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/media/ndk/NdkMediaCodec.cpp b/media/ndk/NdkMediaCodec.cpp
index cd0c462..e954ed5 100644
--- a/media/ndk/NdkMediaCodec.cpp
+++ b/media/ndk/NdkMediaCodec.cpp
@@ -59,7 +59,7 @@
 private:
     AMediaCodec* mCodec;
 public:
-    CodecHandler(AMediaCodec *codec);
+    explicit CodecHandler(AMediaCodec *codec);
     virtual void onMessageReceived(const sp<AMessage> &msg);
 };