Fix memory leak in simple-offsetimagefilter

gm/offsetimagefilter.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 "sk_tool_utils.h"
 #include "SkBitmapSource.h"
 #include "SkOffsetImageFilter.h"
@@ skipping 125 matching lines @@
             p.setStyle(SkPaint::kFill_Style);
         }
 
         p.setColor(0x660000FF);
         canvas->drawRect(r, p);
 
         if (clipR) {
             canvas->save();
             canvas->clipRect(*clipR);
         }
-        p.setImageFilter(imgf);
+        if (imgf) {
+            p.setImageFilter(imgf)->unref();
+        }
         p.setColor(0x66FF0000);
         canvas->drawRect(r, p);
 
         if (clipR) {
             canvas->restore();
         }
     }
 
     void onDraw(SkCanvas* canvas) override {
         const SkRect r = SkRect::MakeWH(10, 10);
@@ skipping 22 matching lines @@
         this->doDraw(canvas, r, SkOffsetImageFilter::Create(5, 5, NULL, NULL), &clipR);
         
         canvas->translate(20, 0);
         this->doDraw(canvas, r, SkOffsetImageFilter::Create(10, 0, NULL, &cr2), NULL);
     }
 
 private:
     typedef skiagm::GM INHERITED;
 };
 DEF_GM( return new SimpleOffsetImageFilterGM; )