Make SkImageFilter methods const.

src/core/SkImageFilterUtils.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 "SkMatrix.h"
 
 #if SK_SUPPORT_GPU
 #include "GrTexture.h"
 #include "SkImageFilterUtils.h"
 #include "SkBitmap.h"
 #include "SkGrPixelRef.h"
 #include "SkGr.h"
 
 bool SkImageFilterUtils::WrapTexture(GrTexture* texture, int width, int height, SkBitmap* result) {
     SkImageInfo info = SkImageInfo::MakeN32Premul(width, height);
     result->setConfig(info);
     result->setPixelRef(SkNEW_ARGS(SkGrPixelRef, (info, texture)))->unref();
     return true;
 }
 
-bool SkImageFilterUtils::GetInputResultGPU(SkImageFilter* filter, SkImageFilter::Proxy* proxy,
+bool SkImageFilterUtils::GetInputResultGPU(const SkImageFilter* filter, SkImageFilter::Proxy* proxy,
                                            const SkBitmap& src, const SkMatrix& ctm,
                                            SkBitmap* result, SkIPoint* offset) {
     // Ensure that GrContext calls under filterImage and filterImageGPU below will see an identity
     // matrix with no clip and that the matrix, clip, and render target set before this function was
     // called are restored before we return to the caller.
     GrContext* context = src.getTexture()->getContext();
     GrContext::AutoWideOpenIdentityDraw awoid(context, NULL);
     if (!filter) {
         offset->fX = offset->fY = 0;
         *result = src;
@@ skipping 11 matching lines @@
                 result->setPixelRef(new SkGrPixelRef(info, resultTex))->unref();
                 GrUnlockAndUnrefCachedBitmapTexture(resultTex);
             }
             return true;
         } else {
             return false;
         }
     }
 }
 #endif