Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: I080090d50f1a368a4e7c1a0732297bb6a295e34f
diff --git a/libs/hwui/tests/unit/RenderNodeTests.cpp b/libs/hwui/tests/unit/RenderNodeTests.cpp
index b2997df..43ee654 100644
--- a/libs/hwui/tests/unit/RenderNodeTests.cpp
+++ b/libs/hwui/tests/unit/RenderNodeTests.cpp
@@ -55,7 +55,7 @@
 TEST(RenderNode, releasedCallback) {
     class DecRefOnReleased : public GlFunctorLifecycleListener {
     public:
-        DecRefOnReleased(int* refcnt) : mRefCnt(refcnt) {}
+        explicit DecRefOnReleased(int* refcnt) : mRefCnt(refcnt) {}
         void onGlFunctorReleased(Functor* functor) override {
             *mRefCnt -= 1;
         }