Don't create a GXPFactory when blend is SrcOver

tests/TessellatingPathRendererTests.cpp

Index: tests/TessellatingPathRendererTests.cpp
diff --git a/tests/TessellatingPathRendererTests.cpp b/tests/TessellatingPathRendererTests.cpp
index 219397bc119ba9c24a85a1418ef8eeec598d1d5e..a6eabfdaaf0b422c7a94b08734f55c897c680fee 100644
--- a/tests/TessellatingPathRendererTests.cpp
+++ b/tests/TessellatingPathRendererTests.cpp
@@ -236,6 +236,8 @@ static void test_path(GrDrawTarget* dt, GrRenderTarget* rt, GrResourceProvider*
                       const SkPath& path) {
     GrTessellatingPathRenderer tess;
     GrPipelineBuilder pipelineBuilder;
+    pipelineBuilder.setXPFactory(
+        GrPorterDuffXPFactory::Create(SkXfermode::kSrc_Mode))->unref();
     pipelineBuilder.setRenderTarget(rt);
     GrStrokeInfo stroke(SkStrokeRec::kFill_InitStyle);
     GrPathRenderer::DrawPathArgs args;