Make SkImageFilter methods const.

src/effects/SkDropShadowImageFilter.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 "SkDropShadowImageFilter.h"
 
 #include "SkBitmap.h"
@@ skipping 40 matching lines @@
 void SkDropShadowImageFilter::flatten(SkWriteBuffer& buffer) const
 {
     this->INHERITED::flatten(buffer);
     buffer.writeScalar(fDx);
     buffer.writeScalar(fDy);
     buffer.writeScalar(fSigmaX);
     buffer.writeScalar(fSigmaY);
     buffer.writeColor(fColor);
 }
 
-bool SkDropShadowImageFilter::onFilterImage(Proxy* proxy, const SkBitmap& source, const SkMatrix& matrix, SkBitmap* result, SkIPoint* offset)
+bool SkDropShadowImageFilter::onFilterImage(Proxy* proxy, const SkBitmap& source, const SkMatrix& matrix, SkBitmap* result, SkIPoint* offset) const
 {
     SkBitmap src = source;
     SkIPoint srcOffset = SkIPoint::Make(0, 0);
     if (getInput(0) && !getInput(0)->filterImage(proxy, source, matrix, &src, &srcOffset))
         return false;
 
     SkIRect bounds;
     src.getBounds(&bounds);
     bounds.offset(srcOffset);
     if (!this->applyCropRect(&bounds, matrix)) {
@@ skipping 52 matching lines @@
     bounds.offset(-SkScalarCeilToInt(offsetVec.x()),
                   -SkScalarCeilToInt(offsetVec.y()));
     SkVector sigma, localSigma = SkVector::Make(fSigmaX, fSigmaY);
     ctm.mapVectors(&sigma, &localSigma, 1);
     bounds.outset(SkScalarCeilToInt(SkScalarMul(sigma.x(), SkIntToScalar(3))),
                   SkScalarCeilToInt(SkScalarMul(sigma.y(), SkIntToScalar(3))));
     bounds.join(src);
     *dst = bounds;
     return true;
 }