Add toString methods to SkImageFilter-derived classes

src/effects/SkXfermodeImageFilter.cpp

Index: src/effects/SkXfermodeImageFilter.cpp
diff --git a/src/effects/SkXfermodeImageFilter.cpp b/src/effects/SkXfermodeImageFilter.cpp
index 00e9ed639b0f790b7b4e9b3c369af73da947916c..617593eae6e559b300a6f435f6f0bb0642b4a74f 100644
--- a/src/effects/SkXfermodeImageFilter.cpp
+++ b/src/effects/SkXfermodeImageFilter.cpp
@@ -98,6 +98,17 @@ bool SkXfermodeImageFilter::onFilterImage(Proxy* proxy,
     return true;
 }
 
+#ifndef SK_IGNORE_TO_STRING
+void SkXfermodeImageFilter::toString(SkString* str) const {
+    str->appendf("SkXfermodeImageFilter: (");
+    str->appendf("xfermode: (");
+    if (fMode) {
+        fMode->toString(str);
+    }
+    str->append("))");
+}
+#endif
+
 #if SK_SUPPORT_GPU
 
 bool SkXfermodeImageFilter::canFilterImageGPU() const {
@@ -165,3 +176,4 @@ bool SkXfermodeImageFilter::filterImageGPU(Proxy* proxy,
 }
 
 #endif
+