Add toString methods to SkImageFilter-derived classes

gm/imagefiltersgraph.cpp

Index: gm/imagefiltersgraph.cpp
diff --git a/gm/imagefiltersgraph.cpp b/gm/imagefiltersgraph.cpp
index 8469a43b59e824d52d02d29a377c9edb59ed3149..ae6f4a6d1fa809a510a6afceea2b8c70d7a985ee 100644
--- a/gm/imagefiltersgraph.cpp
+++ b/gm/imagefiltersgraph.cpp
@@ -62,6 +62,7 @@ public:
         return true;
     }
 
+    SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SimpleOffsetFilter);
 
 protected:
@@ -89,6 +90,13 @@ SkFlattenable* SimpleOffsetFilter::CreateProc(SkReadBuffer& buffer) {
     return Create(dx, dy, common.getInput(0));
 }
 
+#ifndef SK_IGNORE_TO_STRING
+void SimpleOffsetFilter::toString(SkString* str) const {
+    str->appendf("SimpleOffsetFilter: (");
+    str->append(")");
+}
+#endif
+
 class ImageFiltersGraphGM : public skiagm::GM {
 public:
     ImageFiltersGraphGM() {}