Reland "Track field types.".

src/arm64/lithium-codegen-arm64.cc

Index: src/arm64/lithium-codegen-arm64.cc
diff --git a/src/arm64/lithium-codegen-arm64.cc b/src/arm64/lithium-codegen-arm64.cc
index 1fb5b7632e79110e147570308d951d97a3479890..292c7a0f287fc9bd904811b5f9c6673a9a6e392f 100644
--- a/src/arm64/lithium-codegen-arm64.cc
+++ b/src/arm64/lithium-codegen-arm64.cc
@@ -5265,7 +5265,7 @@ void LCodeGen::DoStoreNamedField(LStoreNamedField* instr) {
       !instr->hydrogen()->value()->type().IsHeapObject()) {
     DeoptimizeIfSmi(value, instr->environment());
 
-    // 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;
   }