Port SkBlurImage opts to SkOpts.

src/core/SkOpts.h

Index: src/core/SkOpts.h
diff --git a/src/core/SkOpts.h b/src/core/SkOpts.h
index 9239f8efec9dfe20c8dca5f64fc4d8d5e59e95af..12f3d151eb4a0452a3048557d31bd13ca1b170e7 100644
--- a/src/core/SkOpts.h
+++ b/src/core/SkOpts.h
@@ -30,6 +30,10 @@ namespace SkOpts {
 
     // May return nullptr if we haven't specialized the given Mode.
     extern SkXfermode* (*create_xfermode)(const ProcCoeff&, SkXfermode::Mode);
+
+    // BoxBlurs may be nullptr if not specialized.
+    typedef void (*BoxBlur)(const SkPMColor*, int, SkPMColor*, int, int, int, int, int);
+    extern BoxBlur box_blur_xx, box_blur_xy, box_blur_yx;
 }
 
 #endif//SkOpts_DEFINED