Fix google-explicit-constructor warnings.

* Add explicit keyword to conversion constructors.
Bug: 28341362
Test: build with WITH_TIDY=1

Change-Id: Ic550902559b0800bdcfc0b1d301313a909434eed
diff --git a/libs/input/SpriteController.h b/libs/input/SpriteController.h
index 905833c..7fc8d6f 100644
--- a/libs/input/SpriteController.h
+++ b/libs/input/SpriteController.h
@@ -214,7 +214,7 @@
         virtual ~SpriteImpl();
 
     public:
-        SpriteImpl(const sp<SpriteController> controller);
+        explicit SpriteImpl(const sp<SpriteController> controller);
 
         virtual void setIcon(const SpriteIcon& icon);
         virtual void setVisible(bool visible);