Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I625fbab25f16282c2ea929cd16283d9d146fa17b
diff --git a/media/libmedia/IMediaHTTPConnection.cpp b/media/libmedia/IMediaHTTPConnection.cpp
index 0dda0be9..e4b717b 100644
--- a/media/libmedia/IMediaHTTPConnection.cpp
+++ b/media/libmedia/IMediaHTTPConnection.cpp
@@ -38,7 +38,7 @@
 };
 
 struct BpMediaHTTPConnection : public BpInterface<IMediaHTTPConnection> {
-    BpMediaHTTPConnection(const sp<IBinder> &impl)
+    explicit BpMediaHTTPConnection(const sp<IBinder> &impl)
         : BpInterface<IMediaHTTPConnection>(impl) {
     }