Revert of change all factories to return their base-class

bench/MatrixConvolutionBench.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 "SkMatrixConvolutionImageFilter.h"
 #include "SkPaint.h"
@@ skipping 32 matching lines @@
         for (int i = 0; i < loops; i++) {
             SkRect r = SkRect::MakeWH(rand.nextUScalar1() * 400,
                                       rand.nextUScalar1() * 400);
             paint.setImageFilter(fFilter);
             canvas->drawOval(r, paint);
         }
     }
 
 private:
     typedef Benchmark INHERITED;
-    SkImageFilter* fFilter;
+    SkMatrixConvolutionImageFilter* fFilter;
     SkString fName;
 };
 
 DEF_BENCH( return new MatrixConvolutionBench(SkMatrixConvolutionImageFilter::kClamp_TileMode, true); )
 DEF_BENCH( return new MatrixConvolutionBench(SkMatrixConvolutionImageFilter::kRepeat_TileMode, true); )
 DEF_BENCH( return new MatrixConvolutionBench(SkMatrixConvolutionImageFilter::kClampToBlack_TileMode, true); )
 DEF_BENCH( return new MatrixConvolutionBench(SkMatrixConvolutionImageFilter::kClampToBlack_TileMode, false); )