use ClipOp instead of SkRegion for clipping

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 71 matching lines @@
     }
     SkCanvas canvas(device);
     canvas.translate(SkIntToScalar(-bounds.left()), SkIntToScalar(-bounds.top()));
     SkPaint paint;
     paint.setXfermodeMode(SkXfermode::kSrc_Mode);
     canvas.drawBitmap(background, SkIntToScalar(backgroundOffset.fX),
                       SkIntToScalar(backgroundOffset.fY), &paint);
     paint.setXfermode(fMode);
     canvas.drawBitmap(foreground, SkIntToScalar(foregroundOffset.fX),
                       SkIntToScalar(foregroundOffset.fY), &paint);
-    canvas.clipRect(SkRect::Make(foregroundBounds), SkRegion::kDifference_Op);
+    canvas.clipRect(SkRect::Make(foregroundBounds), kDifference_SkClipOp);
     paint.setColor(SK_ColorTRANSPARENT);
     canvas.drawPaint(paint);
     *dst = device->accessBitmap(false);
     offset->fX = bounds.left();
     offset->fY = bounds.top();
     return true;
 }
 
 #if SK_SUPPORT_GPU
 
@@ skipping 55 matching lines @@
     paint.addColorProcessor(xferProcessor)->unref();
     context->drawRect(paint, srcRect);
 
     offset->fX = backgroundOffset.fX;
     offset->fY = backgroundOffset.fY;
     WrapTexture(dst, src.width(), src.height(), result);
     return true;
 }
 
 #endif