Lower simplified StringAdd to stub call.

src/compiler/simplified-lowering.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_COMPILER_SIMPLIFIED_LOWERING_H_
 #define V8_COMPILER_SIMPLIFIED_LOWERING_H_
 
 #include "src/compiler/js-graph.h"
 #include "src/compiler/machine-operator.h"
 #include "src/compiler/node.h"
 #include "src/compiler/simplified-operator.h"
 
 namespace v8 {
 namespace internal {
 namespace compiler {
 
 class SimplifiedLowering {
  public:
   explicit SimplifiedLowering(JSGraph* jsgraph)
       : jsgraph_(jsgraph), machine_(jsgraph->zone()) {}
   virtual ~SimplifiedLowering() {}
 
   void LowerAllNodes();
 
   // TODO(titzer): These are exposed for direct testing. Use a friend class.
   void DoLoadField(Node* node);
   void DoStoreField(Node* node);
   void DoLoadElement(Node* node);
   void DoStoreElement(Node* node);
+  void DoStringAdd(Node* node);
 
  private:
   JSGraph* jsgraph_;
   MachineOperatorBuilder machine_;
 
   Node* SmiTag(Node* node);
   Node* IsTagged(Node* node);
   Node* Untag(Node* node);
   Node* OffsetMinusTagConstant(int32_t offset);
   Node* ComputeIndex(const ElementAccess& access, Node* index);
 
   friend class RepresentationSelector;
 
   Zone* zone() { return jsgraph_->zone(); }
   JSGraph* jsgraph() { return jsgraph_; }
   Graph* graph() { return jsgraph()->graph(); }
   CommonOperatorBuilder* common() { return jsgraph()->common(); }
   MachineOperatorBuilder* machine() { return &machine_; }
 };
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_COMPILER_SIMPLIFIED_LOWERING_H_