change pixelref to not inherit from SkFlattenable

src/ports/SkGlobalInitialization_default.cpp

Index: src/ports/SkGlobalInitialization_default.cpp
diff --git a/src/ports/SkGlobalInitialization_default.cpp b/src/ports/SkGlobalInitialization_default.cpp
index b08906aeff5012406d8d7ffc4c287d8073756703..5c693af13fbff4707c4d07518f4984bd4e83be39 100644
--- a/src/ports/SkGlobalInitialization_default.cpp
+++ b/src/ports/SkGlobalInitialization_default.cpp
@@ -106,7 +106,9 @@ static void InitializeFlattenables() {
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkMergeImageFilter)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkColorFilterImageFilter)
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkDownSampleImageFilter)
+#ifdef SK_SUPPORT_LEGACY_PIXELREF_UNFLATTENABLE
     SK_DEFINE_FLATTENABLE_REGISTRAR_ENTRY(SkMallocPixelRef)
+#endif
 
     SkArithmeticMode::InitializeFlattenables();
     SkBlurMaskFilter::InitializeFlattenables();