Make SkPixelXorXfermode's opColor be SkPMColor

include/effects/SkPixelXorXfermode.h

 /*
  * Copyright 2007 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkPixelXorXfermode_DEFINED
 #define SkPixelXorXfermode_DEFINED
 
@@ skipping 18 matching lines @@
 #endif
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkPixelXorXfermode)
 
 protected:
     void flatten(SkWriteBuffer&) const override;
     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;
 };
 
 #endif