Don't create a GXPFactory when blend is SrcOver

src/effects/SkXfermodeImageFilter.cpp

 /*
  * Copyright 2013 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.
  */
 
 #include "SkXfermodeImageFilter.h"
 #include "SkCanvas.h"
 #include "SkDevice.h"
@@ skipping 173 matching lines @@
         foregroundTex, foregroundMatrix,
         GrTextureDomain::MakeTexelDomain(foregroundTex, foreground.bounds()),
         GrTextureDomain::kDecal_Mode,
         GrTextureParams::kNone_FilterMode)
     );
 
     paint.addColorFragmentProcessor(foregroundDomain.get());
     if (xferFP) {
         paint.addColorFragmentProcessor(xferFP)->unref();
     }
+    paint.setPorterDuffXPFactory(SkXfermode::kSrc_Mode);
 
     SkAutoTUnref<GrDrawContext> drawContext(context->drawContext(dst->asRenderTarget()));
     if (!drawContext) {
         return false;
     }
 
     drawContext->drawRect(GrClip::WideOpen(), paint, SkMatrix::I(), srcRect);
 
     offset->fX = backgroundOffset.fX;
     offset->fY = backgroundOffset.fY;
     WrapTexture(dst, src.width(), src.height(), result);
     return true;
 }
 
 #endif