Add toString methods to SkImageFilter-derived classes

src/effects/SkTileImageFilter.cpp

Index: src/effects/SkTileImageFilter.cpp
diff --git a/src/effects/SkTileImageFilter.cpp b/src/effects/SkTileImageFilter.cpp
index d640ac7adbd969331c8a43e98b15dddc64027b39..669c234d95c7934b456cc6ba208faf8e0286fd40 100644
--- a/src/effects/SkTileImageFilter.cpp
+++ b/src/effects/SkTileImageFilter.cpp
@@ -106,3 +106,10 @@ void SkTileImageFilter::flatten(SkWriteBuffer& buffer) const {
     buffer.writeRect(fSrcRect);
     buffer.writeRect(fDstRect);
 }
+
+#ifndef SK_IGNORE_TO_STRING
+void SkTileImageFilter::toString(SkString* str) const {
+    str->appendf("SkTileImageFilter: (");
+    str->append(")");
+}
+#endif