Consistently use HStringAdd instead of HCallStub with CodeStub::StringAdd.

src/hydrogen-instructions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // 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 6163 matching lines @@
   ElementsKind from_kind_;
   ElementsKind to_kind_;
 };
 
 
 class HStringAdd: public HBinaryOperation {
  public:
   static HInstruction* New(Zone* zone,
                            HValue* context,
                            HValue* left,
-                           HValue* right);
+                           HValue* right,
+                           StringAddFlags flags = NO_STRING_CHECK_IN_STUB);
+
+  StringAddFlags flags() const { return flags_; }
 
   virtual Representation RequiredInputRepresentation(int index) {
     return Representation::Tagged();
   }
 
   virtual HType CalculateInferredType() {
     return HType::String();
   }
 
   DECLARE_CONCRETE_INSTRUCTION(StringAdd)
 
  protected:
   virtual bool DataEquals(HValue* other) { return true; }
 
-
  private:
-  HStringAdd(HValue* context, HValue* left, HValue* right)
-      : HBinaryOperation(context, left, right) {
+  HStringAdd(HValue* context, HValue* left, HValue* right, StringAddFlags flags)
+      : HBinaryOperation(context, left, right), flags_(flags) {
     set_representation(Representation::Tagged());
     SetFlag(kUseGVN);
     SetGVNFlag(kDependsOnMaps);
     SetGVNFlag(kChangesNewSpacePromotion);
   }
 
   // TODO(svenpanne) Might be safe, but leave it out until we know for sure.
   //  virtual bool IsDeletable() const { return true; }
+
+  const StringAddFlags flags_;
 };
 
 
 class HStringCharCodeAt: public HTemplateInstruction<3> {
  public:
   HStringCharCodeAt(HValue* context, HValue* string, HValue* index) {
     SetOperandAt(0, context);
     SetOperandAt(1, string);
     SetOperandAt(2, index);
     set_representation(Representation::Integer32());
@@ skipping 460 matching lines @@
   virtual bool IsDeletable() const { return true; }
 };
 
 
 #undef DECLARE_INSTRUCTION
 #undef DECLARE_CONCRETE_INSTRUCTION
 
 } }  // namespace v8::internal
 
 #endif  // V8_HYDROGEN_INSTRUCTIONS_H_