Implement crop rect support for the merge image filter.

include/effects/SkMergeImageFilter.h

 /*
  * Copyright 2012 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkMergeImageFilter_DEFINED
 #define SkMergeImageFilter_DEFINED
 
 #include "SkImageFilter.h"
 
 #include "SkXfermode.h"
 
 class SK_API SkMergeImageFilter : public SkImageFilter {
 public:
     SkMergeImageFilter(SkImageFilter* first, SkImageFilter* second,
-                       SkXfermode::Mode = SkXfermode::kSrcOver_Mode);
+                       SkXfermode::Mode = SkXfermode::kSrcOver_Mode,
+                       const SkIRect* cropRect = NULL);
     SkMergeImageFilter(SkImageFilter* filters[], int count,
-                       const SkXfermode::Mode modes[] = NULL);
+                       const SkXfermode::Mode modes[] = NULL,
+                       const SkIRect* cropRect = NULL);
     virtual ~SkMergeImageFilter();
 
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkMergeImageFilter)
 
 protected:
     SkMergeImageFilter(SkFlattenableReadBuffer& buffer);
     virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
 
     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;
 
 private:
     uint8_t*            fModes; // SkXfermode::Mode
 
     // private storage, to avoid dynamically allocating storage for our copy
     // of the modes (unless the count is so large we can't fit).
     intptr_t    fStorage[16];
 
     void initAllocModes();
     void initModes(const SkXfermode::Mode []);
 
     typedef SkImageFilter INHERITED;
 };
 
 #endif