Add MIPS SIMD Arch (MSA) optimized MirrorRow function

libyuv.gni

 # Copyright 2016 The LibYuv Project Authors. All rights reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS. All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 import("//build_overrides/build.gni")
 import("//build/config/arm.gni")
+import("//build/config/mips.gni")
 
 declare_args() {
   libyuv_include_tests = !build_with_chromium
   libyuv_disable_jpeg = false
   libyuv_use_neon = (current_cpu == "arm64" ||
       (current_cpu == "arm" && (arm_use_neon || arm_optionally_use_neon)))
+  libyuv_use_msa = (current_cpu == "mips64el" || current_cpu == "mipsel") &&
+    mips_use_msa
 }