Simplify flattening to just write enough to call the factory

src/effects/SkLumaColorFilter.cpp

Index: src/effects/SkLumaColorFilter.cpp
diff --git a/src/effects/SkLumaColorFilter.cpp b/src/effects/SkLumaColorFilter.cpp
index d33e5e8d78ea0087c2fc9ded6656b797afa0ddde..26621bb02e898776bfb484c693719f16dd143408 100644
--- a/src/effects/SkLumaColorFilter.cpp
+++ b/src/effects/SkLumaColorFilter.cpp
@@ -41,17 +41,18 @@ SkColorFilter* SkLumaColorFilter::Create() {
     return SkNEW(SkLumaColorFilter);
 }
 
-SkLumaColorFilter::SkLumaColorFilter()
-    : INHERITED() {
-}
+SkLumaColorFilter::SkLumaColorFilter() : INHERITED() {}
 
-SkLumaColorFilter::SkLumaColorFilter(SkReadBuffer& buffer)
-    : INHERITED(buffer) {
-}
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
+SkLumaColorFilter::SkLumaColorFilter(SkReadBuffer& buffer) : INHERITED(buffer) {}
+#endif
 
-void SkLumaColorFilter::flatten(SkWriteBuffer&) const {
+SkFlattenable* SkLumaColorFilter::CreateProc(SkReadBuffer&) {
+    return SkNEW(SkLumaColorFilter);
 }
 
+void SkLumaColorFilter::flatten(SkWriteBuffer&) const {}
+
 #ifndef SK_IGNORE_TO_STRING
 void SkLumaColorFilter::toString(SkString* str) const {
     str->append("SkLumaColorFilter ");