Add MIPS SIMD Arch (MSA) optimized MirrorRow function

libyuv.gni

Index: libyuv.gni
diff --git a/libyuv.gni b/libyuv.gni
index 2f6930d76f20d11d2d1ddfc589cfe7f2ac643224..89e4d38232767e84c5fa76498a1edf21acfa6087 100644
--- a/libyuv.gni
+++ b/libyuv.gni
@@ -8,10 +8,13 @@
 
 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
 }