[csa] Migrate String.prototype.concat to TurboFan builtin.

src/builtins/builtins.h

 // Copyright 2011 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_BUILTINS_BUILTINS_H_
 #define V8_BUILTINS_BUILTINS_H_
 
 #include "src/base/flags.h"
 #include "src/globals.h"
 
@@ skipping 756 matching lines @@
   /* String */                                                                 \
   ASM(StringConstructor)                                                       \
   ASM(StringConstructor_ConstructStub)                                         \
   CPP(StringFromCodePoint)                                                     \
   /* ES6 section 21.1.2.1 String.fromCharCode ( ...codeUnits ) */              \
   TFJ(StringFromCharCode, SharedFunctionInfo::kDontAdaptArgumentsSentinel)     \
   /* ES6 section 21.1.3.1 String.prototype.charAt ( pos ) */                   \
   TFJ(StringPrototypeCharAt, 1)                                                \
   /* ES6 section 21.1.3.2 String.prototype.charCodeAt ( pos ) */               \
   TFJ(StringPrototypeCharCodeAt, 1)                                            \
+  /* ES6 #sec-string.prototype.concat */                                       \
+  TFJ(StringPrototypeConcat, SharedFunctionInfo::kDontAdaptArgumentsSentinel)  \
   /* ES6 section 21.1.3.6 */                                                   \
   /* String.prototype.endsWith ( searchString [ , endPosition ] ) */           \
   CPP(StringPrototypeEndsWith)                                                 \
   /* ES6 section 21.1.3.7 */                                                   \
   /* String.prototype.includes ( searchString [ , position ] ) */              \
   CPP(StringPrototypeIncludes)                                                 \
   /* ES6 section #sec-string.prototype.indexof */                              \
   /* String.prototype.indexOf ( searchString [ , position ] ) */               \
   TFJ(StringPrototypeIndexOf, SharedFunctionInfo::kDontAdaptArgumentsSentinel) \
   /* ES6 section 21.1.3.9 */                                                   \
@@ skipping 269 matching lines @@
 
   friend class Isolate;
 
   DISALLOW_COPY_AND_ASSIGN(Builtins);
 };
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_BUILTINS_BUILTINS_H_