Image filters: implement offsets in GPU path.

include/effects/SkBlendImageFilter.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 SkBlendImageFilter_DEFINED
 #define SkBlendImageFilter_DEFINED
 
@@ skipping 15 matching lines @@
 
     SK_DECLARE_PUBLIC_FLATTENABLE_DESERIALIZATION_PROCS(SkBlendImageFilter)
 
     virtual bool onFilterImage(Proxy* proxy,
                                const SkBitmap& src,
                                const SkMatrix& ctm,
                                SkBitmap* dst,
                                SkIPoint* offset) SK_OVERRIDE;
 #if SK_SUPPORT_GPU
     virtual bool canFilterImageGPU() const SK_OVERRIDE { return true; }
-    virtual bool filterImageGPU(Proxy* proxy, const SkBitmap& src, SkBitmap* result) SK_OVERRIDE;
+    virtual bool filterImageGPU(Proxy* proxy, const SkBitmap& src, SkBitmap* result,
+                                SkIPoint* offset) SK_OVERRIDE;
 #endif
 
 protected:
     explicit SkBlendImageFilter(SkFlattenableReadBuffer& buffer);
     virtual void flatten(SkFlattenableWriteBuffer&) const SK_OVERRIDE;
 
 private:
     Mode fMode;
     typedef SkImageFilter INHERITED;
     SkImageFilter* getBackgroundInput() { return getInput(0); }
     SkImageFilter* getForegroundInput() { return getInput(1); }
 };
 
 #endif