Make SkImageFilter methods const.

src/effects/SkTileImageFilter.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 "SkTileImageFilter.h"
 #include "SkBitmap.h"
 #include "SkCanvas.h"
 #include "SkDevice.h"
 #include "SkReadBuffer.h"
 #include "SkWriteBuffer.h"
 #include "SkMatrix.h"
 #include "SkPaint.h"
 #include "SkShader.h"
 #include "SkValidationUtils.h"
 
 bool SkTileImageFilter::onFilterImage(Proxy* proxy, const SkBitmap& src, const SkMatrix& ctm,
-                                      SkBitmap* dst, SkIPoint* offset) {
+                                      SkBitmap* dst, SkIPoint* offset) const {
     SkBitmap source = src;
     SkImageFilter* input = getInput(0);
     SkIPoint srcOffset = SkIPoint::Make(0, 0);
     if (input && !input->filterImage(proxy, src, ctm, &source, &srcOffset)) {
         return false;
     }
 
     SkRect dstRect;
     ctm.mapRect(&dstRect, fDstRect);
     SkIRect dstIRect;
@@ skipping 48 matching lines @@
     buffer.readRect(&fSrcRect);
     buffer.readRect(&fDstRect);
     buffer.validate(buffer.isValid() && SkIsValidRect(fSrcRect) && SkIsValidRect(fDstRect));
 }
 
 void SkTileImageFilter::flatten(SkWriteBuffer& buffer) const {
     this->INHERITED::flatten(buffer);
     buffer.writeRect(fSrcRect);
     buffer.writeRect(fDstRect);
 }