Get rid of the unused native code StringAddStub.

src/mips/lithium-codegen-mips.cc

 // Copyright 2012 the V8 project authors. All rights reserved.7
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 4426 matching lines @@
   Label no_memento_found;
   __ TestJSArrayForAllocationMemento(object, temp, &no_memento_found,
                                      ne, &no_memento_found);
   DeoptimizeIf(al, instr->environment());
   __ bind(&no_memento_found);
 }
 
 
 void LCodeGen::DoStringAdd(LStringAdd* instr) {
   ASSERT(ToRegister(instr->context()).is(cp));
-  if (FLAG_new_string_add) {
-    ASSERT(ToRegister(instr->left()).is(a1));
-    ASSERT(ToRegister(instr->right()).is(a0));
-    NewStringAddStub stub(instr->hydrogen()->flags(),
-                          isolate()->heap()->GetPretenureMode());
-    CallCode(stub.GetCode(isolate()), RelocInfo::CODE_TARGET, instr);
-  } else {
-    __ push(ToRegister(instr->left()));
-    __ push(ToRegister(instr->right()));
-    StringAddStub stub(instr->hydrogen()->flags());
-    CallCode(stub.GetCode(isolate()), RelocInfo::CODE_TARGET, instr);
-  }
+  ASSERT(ToRegister(instr->left()).is(a1));
+  ASSERT(ToRegister(instr->right()).is(a0));
+  StringAddStub stub(instr->hydrogen()->flags(),
+                     isolate()->heap()->GetPretenureMode());
+  CallCode(stub.GetCode(isolate()), RelocInfo::CODE_TARGET, instr);
 }
 
 
 void LCodeGen::DoStringCharCodeAt(LStringCharCodeAt* instr) {
   class DeferredStringCharCodeAt V8_FINAL : public LDeferredCode {
    public:
     DeferredStringCharCodeAt(LCodeGen* codegen, LStringCharCodeAt* instr)
         : LDeferredCode(codegen), instr_(instr) { }
     virtual void Generate() V8_OVERRIDE {
       codegen()->DoDeferredStringCharCodeAt(instr_);
@@ skipping 1353 matching lines @@
   __ Subu(scratch, result, scratch);
   __ lw(result, FieldMemOperand(scratch,
                                 FixedArray::kHeaderSize - kPointerSize));
   __ bind(&done);
 }
 
 
 #undef __
 
 } }  // namespace v8::internal