Dynamically create stencil buffer when needed.

src/effects/SkMorphologyImageFilter.cpp

 /*
  * Copyright 2012 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 "SkMorphologyImageFilter.h"
 #include "SkBitmap.h"
 #include "SkColorPriv.h"
@@ skipping 639 matching lines @@
                       SkBitmap* dst) {
     SkAutoTUnref<GrTexture> srcTexture(SkRef(input.getTexture()));
     SkASSERT(srcTexture);
     GrContext* context = srcTexture->getContext();
 
     GrContext::AutoClip acs(context, SkRect::MakeWH(SkIntToScalar(srcTexture->width()),
                                                     SkIntToScalar(srcTexture->height())));
 
     SkIRect dstRect = SkIRect::MakeWH(rect.width(), rect.height());
     GrSurfaceDesc desc;
-    desc.fFlags = kRenderTarget_GrSurfaceFlag | kNoStencil_GrSurfaceFlag;
+    desc.fFlags = kRenderTarget_GrSurfaceFlag;
     desc.fWidth = rect.width();
     desc.fHeight = rect.height();
     desc.fConfig = kSkia8888_GrPixelConfig;
     SkIRect srcRect = rect;
 
     if (radius.fWidth > 0) {
         GrTexture* texture = context->refScratchTexture(desc, GrContext::kApprox_ScratchTexMatch);
         if (NULL == texture) {
             return false;
         }
@@ skipping 71 matching lines @@
                                          SkBitmap* result, SkIPoint* offset) const {
     return this->filterImageGPUGeneric(true, proxy, src, ctx, result, offset);
 }
 
 bool SkErodeImageFilter::filterImageGPU(Proxy* proxy, const SkBitmap& src, const Context& ctx,
                                         SkBitmap* result, SkIPoint* offset) const {
     return this->filterImageGPUGeneric(false, proxy, src, ctx, result, offset);
 }
 
 #endif