surfaceflinger: manage RenderEngine with unique_ptr

Test: SurfaceFlinger_test
Change-Id: I603a399b88963acdcd154f721fe64bf59d9032fd
diff --git a/services/surfaceflinger/SurfaceFlinger.h b/services/surfaceflinger/SurfaceFlinger.h
index a01d353..2840774 100644
--- a/services/surfaceflinger/SurfaceFlinger.h
+++ b/services/surfaceflinger/SurfaceFlinger.h
@@ -659,7 +659,7 @@
     const std::string mHwcServiceName; // "default" for real use, something else for testing.
 
     // constant members (no synchronization needed for access)
-    RenderEngine* mRenderEngine;
+    std::unique_ptr<RenderEngine> mRenderEngine;
     nsecs_t mBootTime;
     bool mGpuToCpuSupported;
     sp<EventThread> mEventThread;