Implement GPU occluded blur mask filter

gm/occludedrrectblur.cpp

 /*
  * Copyright 2016 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 "SkBlurMaskFilter.h"
 #include "SkRRect.h"
@@ skipping 28 matching lines @@
             strokeColor = SK_ColorYELLOW;
             occRect = occRect2;
         } else {
             strokeColor = SK_ColorCYAN;
             occRect = occRect3;
         }
     }
 
     // draw the blur
     SkPaint paint;
-    paint.setMaskFilter(SkBlurMaskFilter::Make(kNormal_SkBlurStyle, kBlurSigma)); //, occRect));
+    paint.setMaskFilter(SkBlurMaskFilter::Make(kNormal_SkBlurStyle, kBlurSigma, occRect));
     canvas->drawRRect(rr, paint);
 
     // draw the stroked geometry of the full occluder
     SkPaint stroke;
     stroke.setStyle(SkPaint::kStroke_Style);
     stroke.setColor(SK_ColorBLUE);
     canvas->drawRRect(occRR, stroke);
 
     // draw the geometry of the occluding rect
     stroke.setColor(strokeColor);
@@ skipping 253 matching lines @@
     static const int kWidth = 440;
     static const int kHeight = 440;
 
     typedef GM INHERITED;
 };
 
 //////////////////////////////////////////////////////////////////////////////
 
 DEF_GM(return new OccludedRRectBlurGM;)
 }