Skia side RGB to YUV gpu conversion

src/lazy/SkDiscardablePixelRef.h

Index: src/lazy/SkDiscardablePixelRef.h
diff --git a/src/lazy/SkDiscardablePixelRef.h b/src/lazy/SkDiscardablePixelRef.h
index ae955d6eba1b0a4acba7bec6f54b72a7011c63fd..0dd6f19382a711dc5abb92c3a6adae86b566661a 100644
--- a/src/lazy/SkDiscardablePixelRef.h
+++ b/src/lazy/SkDiscardablePixelRef.h
@@ -36,6 +36,10 @@ protected:
         return fGenerator->refEncodedData();
     }
 
+    virtual SkImageGenerator* getImageGenerator() const SK_OVERRIDE {
+        return fGenerator;
+    }
+
 private:
     SkImageGenerator* const fGenerator;
     SkDiscardableMemory::Factory* const fDMFactory;