Fix SkComposeImageFilter's bounds computation and offset handling

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:
     virtual ~SkComposeImageFilter();
 
     static SkImageFilter* Create(SkImageFilter* outer, SkImageFilter* inner) {
         if (NULL == outer) {
             return SkSafeRef(inner);
         }
         if (NULL == inner) {
             return SkRef(outer);
         }
         SkImageFilter* inputs[2] = { outer, inner };
         return SkNEW_ARGS(SkComposeImageFilter, (inputs));
     }
+    void computeFastBounds(const SkRect& src, SkRect* dst) const SK_OVERRIDE;
 
     SK_TO_STRING_OVERRIDE()
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkComposeImageFilter)
 
 protected:
     explicit SkComposeImageFilter(SkImageFilter* inputs[2]) : INHERITED(2, inputs) {
         SkASSERT(inputs[0]);
         SkASSERT(inputs[1]);
     }
     virtual bool onFilterImage(Proxy*, const SkBitmap& src, const Context&,
                                SkBitmap* result, SkIPoint* loc) const SK_OVERRIDE;
     bool onFilterBounds(const SkIRect&, const SkMatrix&, SkIRect*) const SK_OVERRIDE;
 
 private:
     typedef SkImageFilter INHERITED;
 };
 
 #endif