Optimize CSS box-shadow performance

src/gpu/SkGpuDevice.cpp

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkGpuDevice.h"
 
 #include "effects/GrBicubicEffect.h"
@@ skipping 588 matching lines @@
     if (!SkDraw::DrawToMask(devPath, &clip.getBounds(), filter, &context->getMatrix(), &srcM,
                             SkMask::kComputeBoundsAndRenderImage_CreateMode, style)) {
         return false;
     }
     SkAutoMaskFreeImage autoSrc(srcM.fImage);
 
     if (!filter->filterMask(&dstM, srcM, context->getMatrix(), NULL)) {
         return false;
     }
     // this will free-up dstM when we're done (allocated in filterMask())
-    SkAutoMaskFreeImage autoDst(dstM.fImage);
 
     if (clip.quickReject(dstM.fBounds)) {
         return false;
     }
 
     // we now have a device-aligned 8bit mask in dstM, ready to be drawn using
     // the current clip (and identity matrix) and GrPaint settings
     GrTextureDesc desc;
     desc.fWidth = dstM.fBounds.width();
     desc.fHeight = dstM.fBounds.height();
@@ skipping 1323 matching lines @@
     GrLayerHoister::UnlockLayers(fContext->getLayerCache(), picture);
 
     return true;
 }
 
 SkImageFilter::Cache* SkGpuDevice::getImageFilterCache() {
     // We always return a transient cache, so it is freed after each
     // filter traversal.
     return SkImageFilter::Cache::Create(kDefaultImageFilterCacheSize);
 }