Revert "Mac YUV assembly"

media/base/yuv_row.h

 // Copyright (c) 2009 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // yuv_row internal functions to handle YUV conversion and scaling to RGB.
 // These functions are used from both yuv_convert.cc and yuv_scale.cc.
 
 // TODO(fbarchard): Write function that can handle rotation and scaling.
 
 #ifndef MEDIA_BASE_YUV_ROW_H_
@@ skipping 45 matching lines @@
 // This is the slowest of the scalers.
 void ScaleYUVToRGB32Row(const uint8* y_buf,
                         const uint8* u_buf,
                         const uint8* v_buf,
                         uint8* rgb_buf,
                         int width,
                         int scaled_dx);
 }  // extern "C"
 
 #if !defined(USE_MMX)
-// Windows, Mac and Linux x86 use MMX; x64 and other CPUs do not.
-#if defined(OS_WIN) || defined(ARCH_CPU_X86)
+#if defined(_MSC_VER)
+#define USE_MMX 1
+#elif defined(OS_LINUX) && defined(ARCH_CPU_X86)
 #define USE_MMX 1
 #else
 #define USE_MMX 0
 #endif
 #endif
 
 #if USE_MMX
 #if defined(_MSC_VER)
 #define EMMS() __asm emms
 #else
 #define EMMS() asm("emms")
 #endif
 #else
 #define EMMS()
 #endif
 
 #endif  // MEDIA_BASE_YUV_ROW_H_