Implement byte swapping instructions on MIPS32 and MIPS64.

src/mips/assembler-mips.h

Index: src/mips/assembler-mips.h
diff --git a/src/mips/assembler-mips.h b/src/mips/assembler-mips.h
index c595cc9e2e118f77d40b15d3dd42fd71e0f20064..56fa14e0205b6a7007a4f8f1b2dac2318544567f 100644
--- a/src/mips/assembler-mips.h
+++ b/src/mips/assembler-mips.h
@@ -850,6 +850,10 @@ class Assembler : public AssemblerBase {
   void bitswap(Register rd, Register rt);
   void align(Register rd, Register rs, Register rt, uint8_t bp);
 
+  void wsbh(Register rd, Register rt);
+  void seh(Register rd, Register rt);
+  void seb(Register rd, Register rt);
+
   // --------Coprocessor-instructions----------------
 
   // Load, store, and move.