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

src/core/SkOpts.h

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkOpts_DEFINED
 #define SkOpts_DEFINED
 
@@ skipping 46 matching lines @@
                         RGB_to_RGB1,           // i.e. insert an opaque alpha
                         RGB_to_BGR1,           // i.e. swap RB and insert an opaque alpha
                         gray_to_RGB1,          // i.e. expand to color channels + an opaque alpha
                         grayA_to_RGBA,         // i.e. expand to color channels
                         grayA_to_rgbA,         // i.e. expand to color channels and premultiply
                         inverted_CMYK_to_RGB1, // i.e. convert color space
                         inverted_CMYK_to_BGR1; // i.e. convert color space
 
     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