guard rasterizer and drawlooper setters

samplecode/SampleSlides.cpp

Index: samplecode/SampleSlides.cpp
diff --git a/samplecode/SampleSlides.cpp b/samplecode/SampleSlides.cpp
index ca0d9df13f32896b4cc4e9c358aab7a6ac1cafea..9b054adc2c6e00804a6489fdb34b990ac898677f 100644
--- a/samplecode/SampleSlides.cpp
+++ b/samplecode/SampleSlides.cpp
@@ -544,7 +544,7 @@ static void r6(SkLayerRasterizer::Builder* rastBuilder, SkPaint& p)
     p.setAntiAlias(false);
     SkLayerRasterizer::Builder rastBuilder2;
     r5(&rastBuilder2, p);
-    p.setRasterizer(rastBuilder2.detachRasterizer())->unref();
+    p.setRasterizer(rastBuilder2.detach());
     p.setXfermodeMode(SkXfermode::kClear_Mode);
     rastBuilder->addLayer(p);
 }
@@ -615,7 +615,7 @@ static void apply_shader(SkPaint* paint, int index) {
 
     p.setAntiAlias(true);
     proc(&rastBuilder, p);
-    paint->setRasterizer(rastBuilder.detachRasterizer())->unref();
+    paint->setRasterizer(rastBuilder.detach());
     paint->setColor(SK_ColorBLUE);
 }