Image filters: implement offsets in GPU path.

include/effects/SkImageFilterUtils.h

Index: include/effects/SkImageFilterUtils.h
diff --git a/include/effects/SkImageFilterUtils.h b/include/effects/SkImageFilterUtils.h
index 72a25fef7777c8644c7c5e709a17980891e710ea..5b9f192a0ff9f863e1ec9d1dcfeecc6351bace7c 100644
--- a/include/effects/SkImageFilterUtils.h
+++ b/include/effects/SkImageFilterUtils.h
@@ -28,7 +28,8 @@ public:
      * this function returns src.  If the filter has no GPU implementation, it
      * will be processed in software and uploaded to the GPU.
      */
-    static bool GetInputResultGPU(SkImageFilter* filter, SkImageFilter::Proxy* proxy, const SkBitmap& src, SkBitmap* result);
+    static bool GetInputResultGPU(SkImageFilter* filter, SkImageFilter::Proxy* proxy,
+                                  const SkBitmap& src, SkBitmap* result, SkIPoint* offset);
 };
 
 #endif