Add refcnting to SkClipStack on SkCanvas

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 262 matching lines @@
 
 const SkBitmap& SkGpuDevice::onAccessBitmap() {
     DO_DEFERRED_CLEAR();
     return fLegacyBitmap;
 }
 
 void SkGpuDevice::onAttachToCanvas(SkCanvas* canvas) {
     INHERITED::onAttachToCanvas(canvas);
 
     // Canvas promises that this ptr is valid until onDetachFromCanvas is called
-    fClipData.fClipStack = canvas->getClipStack();
+    fClipData.fClipStack.reset(SkRef(canvas->getClipStack()));
 }
 
 void SkGpuDevice::onDetachFromCanvas() {
     INHERITED::onDetachFromCanvas();
-    fClipData.fClipStack = NULL;
+    fClipData.fClipStack.reset(NULL);
 }
 
 // call this every draw call, to ensure that the context reflects our state,
 // and not the state from some other canvas/device
 void SkGpuDevice::prepareDraw(const SkDraw& draw) {
     SkASSERT(fClipData.fClipStack);
 
     fContext->setRenderTarget(fRenderTarget);
 
     SkASSERT(draw.fClipStack && draw.fClipStack == fClipData.fClipStack);
@@ skipping 1611 matching lines @@
 #endif
 }
 
 SkImageFilter::Cache* SkGpuDevice::getImageFilterCache() {
     // We always return a transient cache, so it is freed after each
     // filter traversal.
     return SkImageFilter::Cache::Create(kDefaultImageFilterCacheSize);
 }
 
 #endif