factories should return baseclass, allowing the impl to specialize

gm/bigtileimagefilter.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkImageSource.h"
 #include "SkSurface.h"
 #include "SkTileImageFilter.h"
@@ skipping 38 matching lines @@
     }
 
     void onDraw(SkCanvas* canvas) override {
         canvas->clear(SK_ColorBLACK);
 
         {
             SkPaint p;
 
             SkRect bound = SkRect::MakeWH(SkIntToScalar(kWidth), SkIntToScalar(kHeight));
             SkAutoTUnref<SkImageFilter> imageSource(SkImageSource::Create(fRedImage));
-            SkAutoTUnref<SkTileImageFilter> tif(SkTileImageFilter::Create(
+            SkAutoTUnref<SkImageFilter> tif(SkTileImageFilter::Create(
                             SkRect::MakeWH(SkIntToScalar(kBitmapSize), SkIntToScalar(kBitmapSize)),
                             SkRect::MakeWH(SkIntToScalar(kWidth), SkIntToScalar(kHeight)),
                             imageSource));
             p.setImageFilter(tif);
 
             canvas->saveLayer(&bound, &p);
             canvas->restore();
         }
 
         {
             SkPaint p2;
 
             SkRect bound2 = SkRect::MakeWH(SkIntToScalar(kBitmapSize), SkIntToScalar(kBitmapSize));
 
-            SkAutoTUnref<SkTileImageFilter> tif2(SkTileImageFilter::Create(
+            SkAutoTUnref<SkImageFilter> tif2(SkTileImageFilter::Create(
                             SkRect::MakeWH(SkIntToScalar(kBitmapSize), SkIntToScalar(kBitmapSize)),
                             SkRect::MakeWH(SkIntToScalar(kBitmapSize), SkIntToScalar(kBitmapSize)),
                             nullptr));
             p2.setImageFilter(tif2);
 
             canvas->translate(320, 320);
             canvas->saveLayer(&bound2, &p2);
             canvas->setMatrix(SkMatrix::I());
 
             SkRect bound3 = SkRect::MakeXYWH(320, 320,
@@ skipping 13 matching lines @@
     SkAutoTUnref<SkImage> fRedImage;
     SkAutoTUnref<SkImage> fGreenImage;
 
     typedef GM INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 DEF_GM(return new BigTileImageFilterGM;)
 }