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

src/full-codegen/x64/full-codegen-x64.cc

Index: src/full-codegen/x64/full-codegen-x64.cc
diff --git a/src/full-codegen/x64/full-codegen-x64.cc b/src/full-codegen/x64/full-codegen-x64.cc
index 9e0ce635e19e2463237788b0b6e0bbbdf0a54c7d..ccc60c419393842bbbec44648bc77bcc1a2de968 100644
--- a/src/full-codegen/x64/full-codegen-x64.cc
+++ b/src/full-codegen/x64/full-codegen-x64.cc
@@ -1010,7 +1010,7 @@ void FullCodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   Label no_descriptors;
 
   __ EnumLength(rdx, rax);
-  __ Cmp(rdx, Smi::FromInt(0));
+  __ Cmp(rdx, Smi::kZero);
   __ j(equal, &no_descriptors);
 
   __ LoadInstanceDescriptors(rax, rcx);
@@ -1021,7 +1021,7 @@ void FullCodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   __ Push(rax);  // Map.
   __ Push(rcx);  // Enumeration cache.
   __ Push(rdx);  // Number of valid entries for the map in the enum cache.
-  __ Push(Smi::FromInt(0));  // Initial index.
+  __ Push(Smi::kZero);  // Initial index.
   __ jmp(&loop);
 
   __ bind(&no_descriptors);
@@ -1037,7 +1037,7 @@ void FullCodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   __ movp(rax, FieldOperand(rax, FixedArray::kLengthOffset));
   __ Push(rax);  // Fixed array length (as smi).
   PrepareForBailoutForId(stmt->PrepareId(), BailoutState::NO_REGISTERS);
-  __ Push(Smi::FromInt(0));  // Initial index.
+  __ Push(Smi::kZero);  // Initial index.
 
   // Generate code for doing the condition check.
   __ bind(&loop);
@@ -2962,7 +2962,7 @@ void FullCodeGenerator::VisitCountOperation(CountOperation* expr) {
   } else {
     // Reserve space for result of postfix operation.
     if (expr->is_postfix() && !context()->IsEffect()) {
-      PushOperand(Smi::FromInt(0));
+      PushOperand(Smi::kZero);
     }
     switch (assign_type) {
       case NAMED_PROPERTY: {