Enable viewer in non-Vulkan builds

tools/viewer/sk_app/android/Window_android.cpp

Index: tools/viewer/sk_app/android/Window_android.cpp
diff --git a/tools/viewer/sk_app/android/Window_android.cpp b/tools/viewer/sk_app/android/Window_android.cpp
index 94ba9b00dfadee00a171a24b5b85fff35f28e298..60d89eb3ece6013a4e9616653bae5a2b21550ccb 100644
--- a/tools/viewer/sk_app/android/Window_android.cpp
+++ b/tools/viewer/sk_app/android/Window_android.cpp
@@ -7,7 +7,9 @@
 
 #include "Window_android.h"
 #include "../GLWindowContext.h"
+#ifdef SK_VULKAN
 #include "../VulkanWindowContext.h"
+#endif
 #include "../RasterWindowContext.h"
 
 namespace sk_app {
@@ -62,15 +64,17 @@ void Window_android::initDisplay(ANativeWindow* window) {
     platformData.fNativeWindow = window;
     switch (fBackendType) {
         case kNativeGL_BackendType:
+        default:
             fWindowContext = GLWindowContext::Create((void*)&platformData, fDisplayParams);
             break;
         case kRaster_BackendType:
             fWindowContext = RasterWindowContext::Create((void*)&platformData, fDisplayParams);
             break;
+#ifdef SK_VULKAN
         case kVulkan_BackendType:
-        default:
             fWindowContext = VulkanWindowContext::Create((void*)&platformData, fDisplayParams);
             break;
+#endif
     }
 }