Align SkLumaColorFilter with the spec.

gm/lumafilter.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 "SkCanvas.h"
 #include "SkGradientShader.h"
@@ skipping 16 matching lines @@
 
 static void draw_scene(SkCanvas* canvas, SkColorFilter* filter,
                        SkXfermode::Mode mode, SkShader* s1,
                        SkShader* s2) {
     SkPaint paint;
     paint.setAntiAlias(true);
     SkRect r, c, bounds = SkRect::MakeWH(kSize, kSize);
 
     c = bounds;
     c.fRight = bounds.centerX();
+    paint.setARGB(0x20, 0, 0, 0xff);
     canvas->drawRect(bounds, paint);
 
     canvas->saveLayer(&bounds, NULL);
 
     r = bounds;
     r.inset(kInset, 0);
     paint.setShader(s1);
     paint.setColor(s1 ? SK_ColorBLACK : SkColorSetA(kColor1, 0x80));
     canvas->drawOval(r, paint);
     if (!s1) {
@@ skipping 96 matching lines @@
 private:
     SkAutoTUnref<SkColorFilter> fFilter;
     SkAutoTUnref<SkShader>      fGr1, fGr2;
 
     typedef skiagm::GM INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 DEF_GM( return SkNEW(LumaFilterGM); )