More cleanup in the Vulkan viewer

tools/vulkan/viewer/GMSlide.h

 /*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #ifndef GMSlide_DEFINED
 #define GMSlide_DEFINED
 
 #include "Slide.h"
 #include "gm.h"
 
 class GMSlide : public Slide {
 public:
     GMSlide(skiagm::GM* gm);
     ~GMSlide() override;
 
     void draw(SkCanvas* canvas) override;
+    bool animate(const SkAnimTimer&) override;
 
 private:
     skiagm::GM* fGM;
 };
 
 
 #endif