Revert of Remove SK_SUPPORT_LEGACY_DEEPFLATTENING.

src/opts/SkXfermode_opts_arm_neon.cpp

Index: src/opts/SkXfermode_opts_arm_neon.cpp
diff --git a/src/opts/SkXfermode_opts_arm_neon.cpp b/src/opts/SkXfermode_opts_arm_neon.cpp
index 7534c986ca284a1cbced5cc05f687f728ca9bdfb..dca58eb53e9ac30b5229ddde0971554ed32e5ca9 100644
--- a/src/opts/SkXfermode_opts_arm_neon.cpp
+++ b/src/opts/SkXfermode_opts_arm_neon.cpp
@@ -742,6 +742,12 @@
 typedef uint8x8x4_t (*SkXfermodeProcSIMD)(uint8x8x4_t src, uint8x8x4_t dst);
 
 extern SkXfermodeProcSIMD gNEONXfermodeProcs[];
+
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
+SkNEONProcCoeffXfermode::SkNEONProcCoeffXfermode(SkReadBuffer& buffer) : INHERITED(buffer) {
+    fProcSIMD = reinterpret_cast<void*>(gNEONXfermodeProcs[this->getMode()]);
+}
+#endif
 
 void SkNEONProcCoeffXfermode::xfer32(SkPMColor* SK_RESTRICT dst,
                                      const SkPMColor* SK_RESTRICT src, int count,