Update SkMergeImageFilter to sk_sp

src/effects/SkTestImageFilters.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 "SkTestImageFilters.h"
 #include "SkCanvas.h"
 #include "SkDevice.h"
@@ skipping 59 matching lines @@
         OwnDeviceCanvas canvas(dev);
 
         canvas.drawBitmapRect(tmp, SkRect::MakeIWH(src.width(), src.height()), nullptr);
         *result = dev->accessBitmap(false);
     }
     return true;
 }
 
 SkFlattenable* SkDownSampleImageFilter::CreateProc(SkReadBuffer& buffer) {
     SK_IMAGEFILTER_UNFLATTEN_COMMON(common, 1);
-    return Create(buffer.readScalar(), common.getInput(0));
+    return Create(buffer.readScalar(), common.getInput(0).get());
 }
 
 void SkDownSampleImageFilter::flatten(SkWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);
     buffer.writeScalar(fScale);
 }
 
 #ifndef SK_IGNORE_TO_STRING
 void SkDownSampleImageFilter::toString(SkString* str) const {
     str->appendf("SkDownSampleImageFilter: (");
     str->append(")");
 }
 #endif