Add Smi::Zero and replace all Smi::FromInt(0) calls

src/field-type.cc

Index: src/field-type.cc
diff --git a/src/field-type.cc b/src/field-type.cc
index b3b24e2c14cd11569650360c49d246aeca828383..16bccf294b7818f496f690bcbfa4d5117c58bcbd 100644
--- a/src/field-type.cc
+++ b/src/field-type.cc
@@ -13,7 +13,7 @@ namespace internal {
 
 // static
 FieldType* FieldType::None() {
-  // Do not Smi::FromInt(0) here or for Any(), as that may translate
+  // Do not Smi::kZero here or for Any(), as that may translate
   // as `nullptr` which is not a valid value for `this`.
   return reinterpret_cast<FieldType*>(Smi::FromInt(2));
 }