Add a TurboFan skeleton for StringAddStub.

src/compiler/code-generator.cc

 // Copyright 2013 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.
 
 #include "src/compiler/code-generator.h"
 
 #include "src/compiler/code-generator-impl.h"
 #include "src/compiler/linkage.h"
 #include "src/compiler/pipeline.h"
 
@@ skipping 31 matching lines @@
       masm_(info->isolate(), NULL, 0),
       resolver_(this),
       safepoints_(code->zone()),
       handlers_(code->zone()),
       deoptimization_states_(code->zone()),
       deoptimization_literals_(code->zone()),
       translations_(code->zone()),
       last_lazy_deopt_pc_(0),
       jump_tables_(nullptr),
       ools_(nullptr),
-      osr_pc_offset_(-1) {
+      osr_pc_offset_(-1),
+      needs_frame_(frame->GetSpillSlotCount() > 0 || code->ContainsCall()) {
   for (int i = 0; i < code->InstructionBlockCount(); ++i) {
     new (&labels_[i]) Label;
   }
 }
 
 
 Handle<Code> CodeGenerator::GenerateCode() {
   CompilationInfo* info = this->info();
 
   // Emit a code line info recording start event.
@@ skipping 600 matching lines @@
     : masm_(gen->masm()), next_(gen->ools_) {
   gen->ools_ = this;
 }
 
 
 OutOfLineCode::~OutOfLineCode() {}
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8