change pixelref to not inherit from SkFlattenable

src/lazy/SkCachingPixelRef.h

Index: src/lazy/SkCachingPixelRef.h
diff --git a/src/lazy/SkCachingPixelRef.h b/src/lazy/SkCachingPixelRef.h
index 9fc71c3616ec35f41eaaa1c644746042aae9763d..193fe454823d9051675ee3fca3a16f49d60f8ab7 100644
--- a/src/lazy/SkCachingPixelRef.h
+++ b/src/lazy/SkCachingPixelRef.h
@@ -48,12 +48,15 @@ protected:
     virtual SkData* onRefEncodedData() SK_OVERRIDE {
         return fImageGenerator->refEncodedData();
     }
+
+#ifdef SK_SUPPORT_LEGACY_PIXELREF_UNFLATTENABLE
     // No need to flatten this object. When flattening an SkBitmap,
     // SkWriteBuffer will check the encoded data and write that
     // instead.
     // Future implementations of SkWriteBuffer will need to
     // special case for onRefEncodedData as well.
     SK_DECLARE_UNFLATTENABLE_OBJECT()
+#endif
 
 private:
     SkImageGenerator* const fImageGenerator;