SkPictureImageFilter - clear local canvas before use

src/effects/SkPictureImageFilter.cpp

 /*
  * Copyright 2013 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkPictureImageFilter.h"
 
 #include "SkCanvas.h"
@@ skipping 159 matching lines @@
         const SkImageInfo info = SkImageInfo::MakeN32(localIBounds.width(), localIBounds.height(),
                                                       kPremul_SkAlphaType);
 
         sk_sp<SkSpecialSurface> localSurface(source->makeSurface(info));
         if (!localSurface) {
             return;
         }
 
         SkCanvas* localCanvas = localSurface->getCanvas();
         SkASSERT(localCanvas);
+        
+        localCanvas->clear(0x0);
 
         localCanvas->translate(-SkIntToScalar(localIBounds.fLeft),
                                -SkIntToScalar(localIBounds.fTop));
         localCanvas->drawPicture(fPicture);
 
         localImg = localSurface->makeImageSnapshot();
         SkASSERT(localImg);
     }
 
     {
@@ skipping 15 matching lines @@
     str->appendf("crop: (%f,%f,%f,%f) ",
                  fCropRect.fLeft, fCropRect.fTop, fCropRect.fRight, fCropRect.fBottom);
     if (fPicture) {
         str->appendf("picture: (%f,%f,%f,%f)",
                      fPicture->cullRect().fLeft, fPicture->cullRect().fTop,
                      fPicture->cullRect().fRight, fPicture->cullRect().fBottom);
     }
     str->append(")");
 }
 #endif