Revert[8] "replace SkXfermode obj with SkBlendMode enum in paints"

tests/WritePixelsTest.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkCanvas.h"
 #include "SkColorPriv.h"
 #include "SkMathPriv.h"
@@ skipping 104 matching lines @@
         for (int y = 0; y < DEV_H; ++y) {
             for (int x = 0; x < DEV_W; ++x) {
                 *bmp.getAddr32(x, y) = get_canvas_color(x, y);
             }
         }
     }
     canvas->save();
     canvas->setMatrix(SkMatrix::I());
     canvas->clipRect(DEV_RECT_S, SkCanvas::kReplace_Op);
     SkPaint paint;
-    paint.setXfermodeMode(SkXfermode::kSrc_Mode);
+    paint.setBlendMode(SkBlendMode::kSrc);
     canvas->drawBitmap(bmp, 0, 0, &paint);
     canvas->restore();
 }
 
 /**
  *  Lucky for us, alpha is always in the same spot (SK_A32_SHIFT), for both RGBA and BGRA.
  *  Thus this routine doesn't need to know the exact colortype
  */
 static uint32_t premul(uint32_t color) {
     unsigned a = SkGetPackedA32(color);
@@ skipping 272 matching lines @@
 DEF_GPUTEST_FOR_RENDERING_CONTEXTS(WritePixels_Gpu, reporter, ctxInfo) {
     const SkImageInfo ii = SkImageInfo::MakeN32Premul(DEV_W, DEV_H);
 
     for (auto& origin : { kTopLeft_GrSurfaceOrigin, kBottomLeft_GrSurfaceOrigin }) {
         sk_sp<SkSurface> surface(SkSurface::MakeRenderTarget(ctxInfo.grContext(), SkBudgeted::kNo,
                                                              ii, 0, origin, nullptr));
         test_write_pixels(reporter, surface.get());
     }
 }
 #endif