Implement correct clipping for image filters.

include/effects/SkComposeImageFilter.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkComposeImageFilter_DEFINED
 #define SkComposeImageFilter_DEFINED
 
 #include "SkImageFilter.h"
 
 class SK_API SkComposeImageFilter : public SkImageFilter {
 public:
     SkComposeImageFilter(SkImageFilter* outer, SkImageFilter* inner) : INHERITED(outer, inner) {}
     virtual ~SkComposeImageFilter();
 
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkComposeImageFilter)
 
 protected:
     explicit SkComposeImageFilter(SkReadBuffer& buffer);
 
     virtual bool onFilterImage(Proxy*, const SkBitmap& src, const SkMatrix&,
                                SkBitmap* result, SkIPoint* loc) SK_OVERRIDE;
-    virtual bool onFilterBounds(const SkIRect&, const SkMatrix&, SkIRect*) SK_OVERRIDE;
+    virtual bool onFilterBounds(const SkIRect&, const SkMatrix&, SkIRect*) const SK_OVERRIDE;
 
 private:
     typedef SkImageFilter INHERITED;
 };
 
 #endif