add cast for tostring

src/effects/SkXfermodeImageFilter.cpp

Index: src/effects/SkXfermodeImageFilter.cpp
diff --git a/src/effects/SkXfermodeImageFilter.cpp b/src/effects/SkXfermodeImageFilter.cpp
index 2335a760fbf285a59b8854563757dae7066e648a..420e6e2ab4e4e7549420bb8b5a9c049dd34c7d6f 100644
--- a/src/effects/SkXfermodeImageFilter.cpp
+++ b/src/effects/SkXfermodeImageFilter.cpp
@@ -188,7 +188,7 @@ void SkXfermodeImageFilter_Base::drawForeground(SkCanvas* canvas, SkSpecialImage
 #ifndef SK_IGNORE_TO_STRING
 void SkXfermodeImageFilter_Base::toString(SkString* str) const {
     str->appendf("SkXfermodeImageFilter: (");
-    str->appendf("blendmode: (%d)", fMode);
+    str->appendf("blendmode: (%d)", (int)fMode);
     if (this->getInput(0)) {
         str->appendf("foreground: (");
         this->getInput(0)->toString(str);