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

src/builtins/builtins-conversion.cc

Index: src/builtins/builtins-conversion.cc
diff --git a/src/builtins/builtins-conversion.cc b/src/builtins/builtins-conversion.cc
index a085b149a3fe085b99631f50e066ace59a65d4bf..c229c42ec4bb47fb47a3834cf1c7545e17b496cd 100644
--- a/src/builtins/builtins-conversion.cc
+++ b/src/builtins/builtins-conversion.cc
@@ -390,7 +390,7 @@ void Builtins::Generate_ToLength(CodeStubAssembler* assembler) {
     assembler->Return(assembler->NumberConstant(kMaxSafeInteger));
 
     assembler->Bind(&return_zero);
-    assembler->Return(assembler->SmiConstant(Smi::FromInt(0)));
+    assembler->Return(assembler->SmiConstant(Smi::kZero));
   }
 }