Make SkImageFilter methods const.

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 29 matching lines @@
 
 void SkXfermodeImageFilter::flatten(SkWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);
     buffer.writeFlattenable(fMode);
 }
 
 bool SkXfermodeImageFilter::onFilterImage(Proxy* proxy,
                                             const SkBitmap& src,
                                             const SkMatrix& ctm,
                                             SkBitmap* dst,
-                                            SkIPoint* offset) {
+                                            SkIPoint* offset) const {
     SkBitmap background = src, foreground = src;
     SkImageFilter* backgroundInput = getInput(0);
     SkImageFilter* foregroundInput = getInput(1);
     SkIPoint backgroundOffset = SkIPoint::Make(0, 0);
     if (backgroundInput &&
         !backgroundInput->filterImage(proxy, src, ctm, &background, &backgroundOffset)) {
         return false;
     }
     SkIPoint foregroundOffset = SkIPoint::Make(0, 0);
     if (foregroundInput &&
@@ skipping 32 matching lines @@
     offset->fY = bounds.top();
     return true;
 }
 
 #if SK_SUPPORT_GPU
 
 bool SkXfermodeImageFilter::filterImageGPU(Proxy* proxy,
                                            const SkBitmap& src,
                                            const SkMatrix& ctm,
                                            SkBitmap* result,
-                                           SkIPoint* offset) {
+                                           SkIPoint* offset) const {
     SkBitmap background;
     SkIPoint backgroundOffset = SkIPoint::Make(0, 0);
     if (!SkImageFilterUtils::GetInputResultGPU(getInput(0), proxy, src, ctm, &background,
                                                &backgroundOffset)) {
         return false;
     }
     GrTexture* backgroundTex = background.getTexture();
     SkBitmap foreground;
     SkIPoint foregroundOffset = SkIPoint::Make(0, 0);
     if (!SkImageFilterUtils::GetInputResultGPU(getInput(1), proxy, src, ctm, &foreground,
@@ skipping 43 matching lines @@
         foregroundPaint.setBlendFunc(sk_blend_to_grblend(sm), sk_blend_to_grblend(dm));
         foregroundPaint.addColorTextureEffect(foregroundTex, foregroundMatrix);
         context->drawRect(foregroundPaint, srcRect);
     }
     offset->fX = backgroundOffset.fX;
     offset->fY = backgroundOffset.fY;
     return SkImageFilterUtils::WrapTexture(dst, src.width(), src.height(), result);
 }
 
 #endif