factories should return baseclass, allowing the impl to specialize

bench/MorphologyBench.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Benchmark.h"
 #include "SkCanvas.h"
 #include "SkMorphologyImageFilter.h"
@@ skipping 45 matching lines @@
 
         paint.setAntiAlias(true);
 
         SkRandom rand;
         for (int i = 0; i < loops; i++) {
             SkRect r = SkRect::MakeWH(rand.nextUScalar1() * 400,
                                       rand.nextUScalar1() * 400);
             r.offset(fRadius, fRadius);
 
             if (fRadius > 0) {
-                SkMorphologyImageFilter* mf = nullptr;
+                SkImageFilter* mf = nullptr;
                 switch (fStyle) {
                 case kDilate_MT:
                     mf = SkDilateImageFilter::Create(SkScalarFloorToInt(fRadius),
                                                     SkScalarFloorToInt(fRadius));
                     break;
                 case kErode_MT:
                     mf = SkErodeImageFilter::Create(SkScalarFloorToInt(fRadius),
                                                     SkScalarFloorToInt(fRadius));
                     break;
                 }
@@ skipping 10 matching lines @@
 DEF_BENCH( return new MorphologyBench(SMALL, kErode_MT); )
 DEF_BENCH( return new MorphologyBench(SMALL, kDilate_MT); )
 
 DEF_BENCH( return new MorphologyBench(BIG, kErode_MT); )
 DEF_BENCH( return new MorphologyBench(BIG, kDilate_MT); )
 
 DEF_BENCH( return new MorphologyBench(REAL, kErode_MT); )
 DEF_BENCH( return new MorphologyBench(REAL, kDilate_MT); )
 
 DEF_BENCH( return new MorphologyBench(0, kErode_MT); )