Use opaque black not transparent black as imagefilter GM background.

gm/bitmapsource.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "gm.h"
 
 #include "SkBitmapSource.h"
@@ skipping 32 matching lines @@
     static void fillRectFiltered(SkCanvas* canvas, const SkRect& clipRect, SkImageFilter* filter) {
         SkPaint paint;
         paint.setImageFilter(filter);
         canvas->save();
         canvas->clipRect(clipRect);
         canvas->drawPaint(paint);
         canvas->restore();
     }
 
     void onDraw(SkCanvas* canvas) override {
-        canvas->clear(0x00000000);
+        canvas->clear(SK_ColorBLACK);
         {
             SkRect srcRect = SkRect::MakeXYWH(20, 20, 30, 30);
             SkRect dstRect = SkRect::MakeXYWH(0, 10, 60, 60);
             SkRect clipRect = SkRect::MakeXYWH(0, 0, 100, 100);
             SkRect bounds;
             fBitmap.getBounds(&bounds);
             SkAutoTUnref<SkImageFilter> bitmapSource(SkBitmapSource::Create(fBitmap));
             SkAutoTUnref<SkImageFilter> bitmapSourceSrcRect(SkBitmapSource::Create(fBitmap, srcRect, srcRect));
             SkAutoTUnref<SkImageFilter> bitmapSourceSrcRectDstRect(SkBitmapSource::Create(fBitmap, srcRect, dstRect));
             SkAutoTUnref<SkImageFilter> bitmapSourceDstRectOnly(SkBitmapSource::Create(fBitmap, bounds, dstRect));
@@ skipping 17 matching lines @@
     }
 
 private:
     SkBitmap fBitmap;
     typedef GM INHERITED;
 };
 
 ///////////////////////////////////////////////////////////////////////////////
 
 DEF_GM( return new BitmapSourceGM; )