Get rid of the unused native code StringAddStub.

src/code-stubs.cc

Index: src/code-stubs.cc
diff --git a/src/code-stubs.cc b/src/code-stubs.cc
index da0a9b6ce6c5b30d7d1a40c1d525bc4764f53a22..c5e00ea44cff454a951b89e29973a0b9f98d29ee 100644
--- a/src/code-stubs.cc
+++ b/src/code-stubs.cc
@@ -269,8 +269,8 @@ void BinaryOpICWithAllocationSiteStub::GenerateAheadOfTime(
 }
 
 
-void NewStringAddStub::PrintBaseName(StringStream* stream) {
-  stream->Add("NewStringAddStub");
+void StringAddStub::PrintBaseName(StringStream* stream) {
+  stream->Add("StringAddStub");
   if ((flags() & STRING_ADD_CHECK_BOTH) == STRING_ADD_CHECK_BOTH) {
     stream->Add("_CheckBoth");
   } else if ((flags() & STRING_ADD_CHECK_LEFT) == STRING_ADD_CHECK_LEFT) {
@@ -781,8 +781,8 @@ void BinaryOpWithAllocationSiteStub::InstallDescriptors(Isolate* isolate) {
 
 
 // static
-void NewStringAddStub::InstallDescriptors(Isolate* isolate) {
-  NewStringAddStub stub(STRING_ADD_CHECK_NONE, NOT_TENURED);
+void StringAddStub::InstallDescriptors(Isolate* isolate) {
+  StringAddStub stub(STRING_ADD_CHECK_NONE, NOT_TENURED);
   InstallDescriptor(isolate, &stub);
 }