Dynamically create stencil buffer when needed.

src/effects/SkDisplacementMapEffect.cpp

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkDisplacementMapEffect.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
@@ skipping 399 matching lines @@
         return false;
     }
     if (!bounds.intersect(displBounds)) {
         return false;
     }
     GrTexture* color = colorBM.getTexture();
     GrTexture* displacement = displacementBM.getTexture();
     GrContext* context = color->getContext();
 
     GrSurfaceDesc desc;
-    desc.fFlags = kRenderTarget_GrSurfaceFlag | kNoStencil_GrSurfaceFlag;
+    desc.fFlags = kRenderTarget_GrSurfaceFlag;
     desc.fWidth = bounds.width();
     desc.fHeight = bounds.height();
     desc.fConfig = kSkia8888_GrPixelConfig;
 
     SkAutoTUnref<GrTexture> dst(
         context->refScratchTexture(desc, GrContext::kApprox_ScratchTexMatch));
 
     if (!dst) {
         return false;
     }
@@ skipping 199 matching lines @@
                                        const GrGLCaps&, GrProcessorKeyBuilder* b) {
     const GrDisplacementMapEffect& displacementMap = proc.cast<GrDisplacementMapEffect>();
 
     uint32_t xKey = displacementMap.xChannelSelector();
     uint32_t yKey = displacementMap.yChannelSelector() << kChannelSelectorKeyBits;
 
     b->add32(xKey | yKey);
 }
 #endif