SW backend for viewer on Windows

tools/viewer/sk_app/win/Window_win.cpp

Index: tools/viewer/sk_app/win/Window_win.cpp
diff --git a/tools/viewer/sk_app/win/Window_win.cpp b/tools/viewer/sk_app/win/Window_win.cpp
index e9905d42cced451cb57b867e7ab15dbcdf89742c..2f7247822c6c67f86397a1e0b6616545ae413168 100644
--- a/tools/viewer/sk_app/win/Window_win.cpp
+++ b/tools/viewer/sk_app/win/Window_win.cpp
@@ -270,9 +270,11 @@ void Window_win::show() {
 bool Window_win::attach(BackendType attachType, const DisplayParams& params) {
     switch (attachType) {
         case kNativeGL_BackendType:
-        default:
             fWindowContext = window_context_factory::NewGLForWin(fHWnd, params);
             break;
+        case kRaster_BackendType:
+            fWindowContext = window_context_factory::NewRasterForWin(fHWnd, params);
+            break;
 #ifdef SK_VULKAN
         case kVulkan_BackendType:
             fWindowContext = window_context_factory::NewVulkanForWin(fHWnd, params);