Dynamically create stencil buffer when needed.

src/effects/SkXfermodeImageFilter.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 "SkXfermodeImageFilter.h"
 #include "SkCanvas.h"
 #include "SkDevice.h"
@@ skipping 127 matching lines @@
     if (getInput(1) && !getInput(1)->getInputResultGPU(proxy, src, ctx, &foreground,
                                                        &foregroundOffset)) {
         return onFilterImage(proxy, src, ctx, result, offset);
     }
     GrTexture* foregroundTex = foreground.getTexture();
     GrContext* context = foregroundTex->getContext();
 
     GrFragmentProcessor* xferProcessor = NULL;
 
     GrSurfaceDesc desc;
-    desc.fFlags = kRenderTarget_GrSurfaceFlag | kNoStencil_GrSurfaceFlag;
+    desc.fFlags = kRenderTarget_GrSurfaceFlag;
     desc.fWidth = src.width();
     desc.fHeight = src.height();
     desc.fConfig = kSkia8888_GrPixelConfig;
     SkAutoTUnref<GrTexture> dst(
         context->refScratchTexture(desc, GrContext::kApprox_ScratchTexMatch));
     if (!dst) {
         return false;
     }
 
     if (!fMode || !fMode->asFragmentProcessor(&xferProcessor, backgroundTex)) {
@@ skipping 16 matching lines @@
     context->drawRect(dst->asRenderTarget(), paint, SkMatrix::I(), srcRect);
 
     offset->fX = backgroundOffset.fX;
     offset->fY = backgroundOffset.fY;
     WrapTexture(dst, src.width(), src.height(), result);
     return true;
 }
 
 #endif