Don't create a GXPFactory when blend is SrcOver
BUG=skia:
Review URL: https://codereview.chromium.org/1471053002
diff --git a/src/effects/SkLightingImageFilter.cpp b/src/effects/SkLightingImageFilter.cpp
index 4bb755e..9b6a20f 100644
--- a/src/effects/SkLightingImageFilter.cpp
+++ b/src/effects/SkLightingImageFilter.cpp
@@ -354,6 +354,7 @@
GrPaint paint;
GrFragmentProcessor* fp = this->getFragmentProcessor(src, matrix, bounds, boundaryMode);
paint.addColorFragmentProcessor(fp)->unref();
+ paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
drawContext->fillRectToRect(clip, paint, SkMatrix::I(), dstRect, srcRect);
}