Don't create a GXPFactory when blend is SrcOver

src/gpu/GrPaint.cpp

Index: src/gpu/GrPaint.cpp
diff --git a/src/gpu/GrPaint.cpp b/src/gpu/GrPaint.cpp
index 6f218a4b0b96dfb2b0ae41c201795808b4acd770..1ec8e502be2a308c513b0afb7ebc025a1d660cdd 100644
--- a/src/gpu/GrPaint.cpp
+++ b/src/gpu/GrPaint.cpp
@@ -50,7 +50,14 @@ bool GrPaint::isConstantBlendedColor(GrColor* color) const {
                                         kRGBA_GrColorComponentFlags, false);
 
     GrXPFactory::InvariantBlendedColor blendedColor;
-    fXPFactory->getInvariantBlendedColor(colorProcInfo, &blendedColor);
+    if (fXPFactory) {
+        fXPFactory->getInvariantBlendedColor(colorProcInfo, &blendedColor);
+    } else {
+        GrPorterDuffXPFactory::SrcOverInvariantBlendedColor(colorProcInfo.color(),
+                                                            colorProcInfo.validFlags(),
+                                                            colorProcInfo.isOpaque(),
+                                                            &blendedColor); 
+    }
 
     if (kRGBA_GrColorComponentFlags == blendedColor.fKnownColorFlags) {
         *color = blendedColor.fKnownColor;