MIPS: Reland "Track field types.".

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index dd05f7de3782ab65282bf130b92eb3a5b4e3d71e..f157f8b22d1e0ad192349aa655f21090061cd243 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -4085,7 +4085,7 @@ void LCodeGen::DoStoreNamedField(LStoreNamedField* instr) {
       __ SmiTst(value, scratch);
       DeoptimizeIf(eq, instr->environment(), scratch, Operand(zero_reg));
 
-      // We know that value is a smi now, so we can omit the check below.
+      // We know now that value is not a smi, so we can omit the check below.
       check_needed = OMIT_SMI_CHECK;
     }
   } else if (representation.IsDouble()) {