Enable viewer in non-Vulkan builds

tools/viewer/sk_app/android/Window_android.cpp

 /*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #include "Window_android.h"
 #include "../GLWindowContext.h"
+#ifdef SK_VULKAN
 #include "../VulkanWindowContext.h"
+#endif
 #include "../RasterWindowContext.h"
 
 namespace sk_app {
 
 Window* Window::CreateNativeWindow(void* platformData) {
     Window_android* window = new Window_android();
     if (!window->init((SkiaAndroidApp*)platformData)) {
         delete window;
         return nullptr;
     }
@@ skipping 34 matching lines @@
     // The creation will be done in initDisplay, which is initiated by kSurfaceCreated event.
     return true;
 }
 
 void Window_android::initDisplay(ANativeWindow* window) {
     SkASSERT(window);
     ContextPlatformData_android platformData;
     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
     }
 }
 
 void Window_android::onDisplayDestroyed() {
     detach();
 }
 
 void Window_android::onInval() {
     fSkiaAndroidApp->postMessage(Message(kContentInvalidated));
 }
 
 void Window_android::paintIfNeeded() {
     if (fWindowContext) { // Check if initDisplay has already been called
         onPaint();
     } else {
         markInvalProcessed();
     }
 }
 
 }   // namespace sk_app