Adding more validation

src/effects/SkXfermodeImageFilter.cpp

Index: src/effects/SkXfermodeImageFilter.cpp
diff --git a/src/effects/SkXfermodeImageFilter.cpp b/src/effects/SkXfermodeImageFilter.cpp
index e8fa0d2787301d0578229dafe173bc7ea80cf6c4..620bde9fdb9d90e2a4f041e6421c748f028bbb85 100644
--- a/src/effects/SkXfermodeImageFilter.cpp
+++ b/src/effects/SkXfermodeImageFilter.cpp
@@ -33,7 +33,7 @@ SkXfermodeImageFilter::~SkXfermodeImageFilter() {
 }
 
 SkXfermodeImageFilter::SkXfermodeImageFilter(SkFlattenableReadBuffer& buffer)
-  : INHERITED(buffer) {
+  : INHERITED(2, buffer) {
     fMode = buffer.readXfermode();
 }