Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/media/libmedia/IMediaCodecList.cpp b/media/libmedia/IMediaCodecList.cpp
index e2df104..9fca9c7 100644
--- a/media/libmedia/IMediaCodecList.cpp
+++ b/media/libmedia/IMediaCodecList.cpp
@@ -38,7 +38,7 @@
 class BpMediaCodecList: public BpInterface<IMediaCodecList>
 {
 public:
-    BpMediaCodecList(const sp<IBinder>& impl)
+    explicit BpMediaCodecList(const sp<IBinder>& impl)
         : BpInterface<IMediaCodecList>(impl)
     {
     }