SkMojo: test linking Skia against the Mojo SDK

dm/DMSrcSink.h

Index: dm/DMSrcSink.h
diff --git a/dm/DMSrcSink.h b/dm/DMSrcSink.h
index d02eeaf101e8c57604d058209d93ba0d20a7242a..1c7babd19500d6c9819e9df551962017af1d0cd4 100644
--- a/dm/DMSrcSink.h
+++ b/dm/DMSrcSink.h
@@ -355,6 +355,12 @@ public:
     Error draw(const Src&, SkBitmap*, SkWStream*, SkString*) const override;
 };
 
+class ViaMojo : public Via {
+public:
+    explicit ViaMojo(Sink* sink) : Via(sink) {}
+    Error draw(const Src&, SkBitmap*, SkWStream*, SkString*) const override;
+};
+
 }  // namespace DM
 
 #endif//DMSrcSink_DEFINED