Add low level support for 12 bit 420, 422 and 444 YUV video frame conversion.

include/libyuv/row.h

Index: include/libyuv/row.h
diff --git a/include/libyuv/row.h b/include/libyuv/row.h
index 227156a195b75fbd3d8e3ccd1d9850d3fde9cd40..2871c6fc26048f26e40659c30c157ac534a67ea8 100644
--- a/include/libyuv/row.h
+++ b/include/libyuv/row.h
@@ -252,7 +252,7 @@ extern "C" {
 #define HAS_ARGBTORGB565ROW_AVX2
 #define HAS_J400TOARGBROW_AVX2
 #define HAS_RGB565TOARGBROW_AVX2
-#define HAS_SHORTTOF16ROW_AVX2
+#define HAS_HALFFLOATROW_AVX2
 #endif
 
 // The following are also available on x64 Visual C.
@@ -1934,8 +1934,8 @@ void ARGBPolynomialRow_AVX2(const uint8* src_argb,
                             int width);
 
 // Scale and convert to half float.
-void ShortToF16Row_C(const uint16* src, int16* dst, float scale, int width);
-void ShortToF16Row_AVX2(const uint16* src, int16* dst, float scale, int width);
+void HalfFloatRow_C(const uint16* src, int16* dst, float scale, int width);
+void HalfFloatRow_AVX2(const uint16* src, int16* dst, float scale, int width);
 
 void ARGBLumaColorTableRow_C(const uint8* src_argb, uint8* dst_argb, int width,
                              const uint8* luma, uint32 lumacoeff);