Fix google-explicit-constructor warnings.

Bug: 28341362
Change-Id: Ibdd6a210bb7ff228e3624cc319169f77aca3b51e
diff --git a/libs/hwui/renderthread/RenderThread.cpp b/libs/hwui/renderthread/RenderThread.cpp
index 64075f1..8301107 100644
--- a/libs/hwui/renderthread/RenderThread.cpp
+++ b/libs/hwui/renderthread/RenderThread.cpp
@@ -129,7 +129,7 @@
 private:
     RenderThread* mRenderThread;
 public:
-    DispatchFrameCallbacks(RenderThread* rt) : mRenderThread(rt) {}
+    explicit DispatchFrameCallbacks(RenderThread* rt) : mRenderThread(rt) {}
 
     virtual void run() override {
         mRenderThread->dispatchFrameCallbacks();