Add OpenGL context to Viewer.

tools/viewer/sk_app/VulkanWindowContext.h

Index: tools/viewer/sk_app/VulkanWindowContext.h
diff --git a/tools/viewer/sk_app/VulkanWindowContext.h b/tools/viewer/sk_app/VulkanWindowContext.h
index ec80a3251d2f080c17b6d8dd7c1acf34b922b740..0d65714bc3927a943a4d9144811d14440803b7a5 100644
--- a/tools/viewer/sk_app/VulkanWindowContext.h
+++ b/tools/viewer/sk_app/VulkanWindowContext.h
@@ -13,9 +13,6 @@
 #include "vk/GrVkBackendContext.h"
 #include "WindowContext.h"
 
-class SkSurface;
-class GrContext;
-
 namespace sk_app {
 
 class VulkanWindowContext : public WindowContext {
@@ -35,11 +32,9 @@ public:
         return ctx;
     }
 
-    SkSurface* getBackbufferSurface() override;
+    sk_sp<SkSurface> getBackbufferSurface() override;
     void swapBuffers() override;
 
-    bool makeCurrent() override { return true; }
-
     bool isValid() override { return SkToBool(fBackendContext.get()); }
 
     void resize(uint32_t w, uint32_t h) override {
@@ -99,15 +94,12 @@ private:
     VkPtr<PFN_vkQueuePresentKHR> fQueuePresentKHR;
     VkPtr<PFN_vkCreateSharedSwapchainsKHR> fCreateSharedSwapchainsKHR;
 
-    GrContext*        fContext;
     VkSurfaceKHR      fSurface;
     VkSwapchainKHR    fSwapchain;
     uint32_t          fPresentQueueIndex;
     VkQueue           fPresentQueue;
     int               fWidth;
     int               fHeight;
-    DisplayParams     fDisplayParams;
-    GrPixelConfig     fPixelConfig;
 
     uint32_t          fImageCount;
     VkImage*          fImages;         // images in the swapchain