Do not use assembly implementations of YUV conversions in MSan builds.

media/base/yuv_convert.cc

Index: media/base/yuv_convert.cc
diff --git a/media/base/yuv_convert.cc b/media/base/yuv_convert.cc
index 893b53df147bf56f4a1b83ba1a9e5dab1683314d..9dc05596e288268c51024d4d4a2de254452edc57 100644
--- a/media/base/yuv_convert.cc
+++ b/media/base/yuv_convert.cc
@@ -132,7 +132,8 @@ void InitializeCPUSpecificYUVConversions() {
   g_convert_yuva_to_argb_proc_ = ConvertYUVAToARGB_C;
   g_empty_register_state_proc_ = EmptyRegisterStateStub;
 
-#if defined(ARCH_CPU_X86_FAMILY)
+  // Assembly code confuses MemorySanitizer.
+#if defined(ARCH_CPU_X86_FAMILY) && !defined(MEMORY_SANITIZER)
   base::CPU cpu;
   if (cpu.has_mmx()) {
     g_convert_yuv_to_rgb32_row_proc_ = ConvertYUVToRGB32Row_MMX;