Implement correct clipping for image filters.

src/effects/SkComposeImageFilter.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 "SkBitmap.h"
 #include "SkComposeImageFilter.h"
 #include "SkReadBuffer.h"
@@ skipping 18 matching lines @@
         return (outer ? outer : inner)->filterImage(proxy, src, ctm, result, offset);
     }
 
     SkBitmap tmp;
     return inner->filterImage(proxy, src, ctm, &tmp, offset) &&
            outer->filterImage(proxy, tmp, ctm, result, offset);
 }
 
 bool SkComposeImageFilter::onFilterBounds(const SkIRect& src,
                                           const SkMatrix& ctm,
-                                          SkIRect* dst) {
+                                          SkIRect* dst) const {
     SkImageFilter* outer = getInput(0);
     SkImageFilter* inner = getInput(1);
 
     if (!outer && !inner) {
         return false;
     }
 
     if (!outer || !inner) {
         return (outer ? outer : inner)->filterBounds(src, ctm, dst);
     }
 
     SkIRect tmp;
     return inner->filterBounds(src, ctm, &tmp) &&
            outer->filterBounds(tmp, ctm, dst);
 }
 
 SkComposeImageFilter::SkComposeImageFilter(SkReadBuffer& buffer)
   : INHERITED(2, buffer) {
 }