tools/skui: put all enums in a common namespace

Change-Id: Icd331e8946d80652750b8b6ea0db65f5f676ac3e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/238058
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>
diff --git a/example/HelloWorld.h b/example/HelloWorld.h
index d88822e..2609d4e 100644
--- a/example/HelloWorld.h
+++ b/example/HelloWorld.h
@@ -22,7 +22,7 @@
 
     void onBackendCreated() override;
     void onPaint(SkSurface*) override;
-    bool onChar(SkUnichar c, ModifierKey modifiers) override;
+    bool onChar(SkUnichar c, skui::ModifierKey modifiers) override;
 
 private:
     void updateTitle();