Simplify flattening to just write enough to call the factory

src/effects/SkXfermodeImageFilter.cpp

Index: src/effects/SkXfermodeImageFilter.cpp
diff --git a/src/effects/SkXfermodeImageFilter.cpp b/src/effects/SkXfermodeImageFilter.cpp
index c876d5f6b3759b89505d114ec6fd292636b667d1..9e7ff798306f2c85ca30ff77e4546bf71678f501 100644
--- a/src/effects/SkXfermodeImageFilter.cpp
+++ b/src/effects/SkXfermodeImageFilter.cpp
@@ -31,10 +31,17 @@ SkXfermodeImageFilter::~SkXfermodeImageFilter() {
     SkSafeUnref(fMode);
 }
 
+#ifdef SK_SUPPORT_LEGACY_DEEPFLATTENING
 SkXfermodeImageFilter::SkXfermodeImageFilter(SkReadBuffer& buffer)
   : INHERITED(2, buffer) {
     fMode = buffer.readXfermode();
 }
+#endif
+
+SkFlattenable* SkXfermodeImageFilter::CreateProc(SkReadBuffer& buffer) {
+    SK_IMAGEFILTER_UNFLATTEN_COMMON(common, 2);
+    return Create(buffer.readXfermode(), common.inputAt(0), common.inputAt(1), &common.cropRect());
+}
 
 void SkXfermodeImageFilter::flatten(SkWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);