Revert of Remove SK_SUPPORT_LEGACY_DEEPFLATTENING.

src/effects/SkArithmeticMode.cpp

Index: src/effects/SkArithmeticMode.cpp
diff --git a/src/effects/SkArithmeticMode.cpp b/src/effects/SkArithmeticMode.cpp
index d1e7472f06e6d73776e67f9547d2ca175c268af4..6fb5241c82ace517ecbc1e507200dd3584c38585 100644
--- a/src/effects/SkArithmeticMode.cpp
+++ b/src/effects/SkArithmeticMode.cpp
@@ -48,6 +48,16 @@
         fK[3] = k4;
         fEnforcePMColor = enforcePMColor;
     }
+
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
+    SkArithmeticMode_scalar(SkReadBuffer& buffer) : INHERITED(buffer) {
+        fK[0] = buffer.readScalar();
+        fK[1] = buffer.readScalar();
+        fK[2] = buffer.readScalar();
+        fK[3] = buffer.readScalar();
+        fEnforcePMColor = buffer.readBool();
+    }
+#endif
 
     virtual void flatten(SkWriteBuffer& buffer) const SK_OVERRIDE {
         buffer.writeScalar(fK[0]);