Adding more validation

src/effects/SkTestImageFilters.cpp

Index: src/effects/SkTestImageFilters.cpp
diff --git a/src/effects/SkTestImageFilters.cpp b/src/effects/SkTestImageFilters.cpp
index 289113133c345241cadc6ae7985fe4a0bd6e65d7..cc6d1adc4303fe5a031180f0ccc3749521a3eb83 100755
--- a/src/effects/SkTestImageFilters.cpp
+++ b/src/effects/SkTestImageFilters.cpp
@@ -76,7 +76,8 @@ void SkDownSampleImageFilter::flatten(SkFlattenableWriteBuffer& buffer) const {
     buffer.writeScalar(fScale);
 }
 
-SkDownSampleImageFilter::SkDownSampleImageFilter(SkFlattenableReadBuffer& buffer) : INHERITED(buffer) {
+SkDownSampleImageFilter::SkDownSampleImageFilter(SkFlattenableReadBuffer& buffer)
+  : INHERITED(1, buffer) {
     fScale = buffer.readScalar();
     buffer.validate(SkScalarIsFinite(fScale));
 }