Make SkPixelXorXfermode's opColor be SkPMColor

include/effects/SkPixelXorXfermode.h

Index: include/effects/SkPixelXorXfermode.h
diff --git a/include/effects/SkPixelXorXfermode.h b/include/effects/SkPixelXorXfermode.h
index c248de6cc1db0207ef32de8f92e8c2d66e211120..4aa78ccf5e417e04fad97e554dbbcf0cc94988b1 100644
--- a/include/effects/SkPixelXorXfermode.h
+++ b/include/effects/SkPixelXorXfermode.h
@@ -36,9 +36,11 @@ protected:
     SkPMColor xferColor(SkPMColor src, SkPMColor dst) const override;
 
 private:
-    explicit SkPixelXorXfermode(SkColor opColor) : fOpColor(opColor) {}
+    explicit SkPixelXorXfermode(SkColor opColor) {
+        fOpColor = SkPreMultiplyColor(opColor | 0xFF000000);
+    }
 
-    SkColor fOpColor;
+    SkPMColor fOpColor;
 
     typedef SkXfermode INHERITED;
 };