Add SSSE3 acceleration for S32_D16_filter_DX

src/opts/SkBitmapProcState_opts_SSSE3.h

Index: src/opts/SkBitmapProcState_opts_SSSE3.h
diff --git a/src/opts/SkBitmapProcState_opts_SSSE3.h b/src/opts/SkBitmapProcState_opts_SSSE3.h
index 74504d8bc65e81b1db22f9c0c236c660376d14b6..c7a9a899236a07161dfcf57d66ece2793e253934 100644
--- a/src/opts/SkBitmapProcState_opts_SSSE3.h
+++ b/src/opts/SkBitmapProcState_opts_SSSE3.h
@@ -23,6 +23,9 @@ void S32_alpha_D32_filter_DXDY_SSSE3(const SkBitmapProcState& s,
                                    const uint32_t* xy,
                                    int count, uint32_t* colors);
 
+void S32_D16_filter_DX_SSSE3(const SkBitmapProcState& s,
+                             const uint32_t* xy,
+                             int count, uint16_t* colors);
 void S32_D16_filter_DXDY_SSSE3(const SkBitmapProcState& s,
                                const uint32_t* xy,
                                int count, uint16_t* colors);