Add a hook for CPU-optimized sRGB-sRGB srcover.

src/core/SkOpts.h

Index: src/core/SkOpts.h
diff --git a/src/core/SkOpts.h b/src/core/SkOpts.h
index 04c9f00de301e7c0277ae1c54858a6facc09fa8e..b8aea4aa348cceb5277f50bf3cac326d6d44e31a 100644
--- a/src/core/SkOpts.h
+++ b/src/core/SkOpts.h
@@ -64,6 +64,10 @@ namespace SkOpts {
 
     extern void (*half_to_float)(float[], const uint16_t[], int);
     extern void (*float_to_half)(uint16_t[], const float[], int);
+
+    // Blend ndst src pixels over dst, where both src and dst point to sRGB pixels (RGBA or BGRA).
+    // If nsrc < ndst, we loop over src to create a pattern.
+    extern void (*srcover_srgb_srgb)(uint32_t* dst, const uint32_t* src, int ndst, int nsrc);
 }
 
 #endif//SkOpts_DEFINED