Make bicubic FP factories return const FPs

src/image/SkImageShader.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmapProcShader.h"
 #include "SkBitmapProvider.h"
 #include "SkImage_Base.h"
@@ skipping 100 matching lines @@
     // are provided by the caller.
     bool doBicubic;
     GrTextureParams::FilterMode textureFilterMode =
     GrSkFilterQualityToGrFilterMode(filterQuality, viewM, this->getLocalMatrix(), &doBicubic);
     GrTextureParams params(tm, textureFilterMode);
     SkAutoTUnref<GrTexture> texture(as_IB(fImage)->asTextureRef(context, params));
     if (!texture) {
         return nullptr;
     }
 
-    SkAutoTUnref<GrFragmentProcessor> inner;
+    SkAutoTUnref<const GrFragmentProcessor> inner;
     if (doBicubic) {
         inner.reset(GrBicubicEffect::Create(texture, matrix, tm));
     } else {
         inner.reset(GrSimpleTextureEffect::Create(texture, matrix, params));
     }
 
     if (GrPixelConfigIsAlphaOnly(texture->config())) {
         return SkRef(inner.get());
     }
     return GrFragmentProcessor::MulOutputByInputAlpha(inner);
 }
 
 #endif