Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I0ce850de85e0de6a5472dd142f738856142db9ec
diff --git a/libs/gui/ISurfaceComposer.cpp b/libs/gui/ISurfaceComposer.cpp
index 78886d5..9bfc906 100644
--- a/libs/gui/ISurfaceComposer.cpp
+++ b/libs/gui/ISurfaceComposer.cpp
@@ -46,7 +46,7 @@
 class BpSurfaceComposer : public BpInterface<ISurfaceComposer>
 {
 public:
-    BpSurfaceComposer(const sp<IBinder>& impl)
+    explicit BpSurfaceComposer(const sp<IBinder>& impl)
         : BpInterface<ISurfaceComposer>(impl)
     {
     }