Add assembler test.

src/mips/macro-assembler-mips.cc

Index: src/mips/macro-assembler-mips.cc
diff --git a/src/mips/macro-assembler-mips.cc b/src/mips/macro-assembler-mips.cc
index 611ed32a9fb11c32c4db724d57f1095e64622fdc..4a127763aefe9a7d6f8d9bea18215b4167b11dbf 100644
--- a/src/mips/macro-assembler-mips.cc
+++ b/src/mips/macro-assembler-mips.cc
@@ -1052,6 +1052,19 @@ void MacroAssembler::Pref(int32_t hint, const MemOperand& rs) {
 }
 
 
+void MacroAssembler::Lsa(Register rd, Register rt, Register rs, uint8_t sa,
+                         Register scratch) {
+  if (IsMipsArchVariant(kMips32r6) && sa <= 4) {
+    lsa(rd, rt, rs, sa);
+  } else {
+    Register tmp = rd.is(rt) ? scratch : rd;
+    DCHECK(!tmp.is(rt));
+    sll(tmp, rs, sa);
+    Addu(rd, rt, tmp);
+  }
+}
+
+
 // ------------Pseudo-instructions-------------
 
 void MacroAssembler::Ulw(Register rd, const MemOperand& rs) {