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

src/bootstrapper.cc

 // 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.
 
 #include "src/bootstrapper.h"
 
 #include "src/accessors.h"
 #include "src/api-natives.h"
 #include "src/base/ieee754.h"
 #include "src/code-stubs.h"
@@ skipping 1670 matching lines @@
 
     // Install the "constructor" property on the {prototype}.
     JSObject::AddProperty(prototype, factory->constructor_string(), string_fun,
                           DONT_ENUM);
 
     // Install the String.prototype methods.
     SimpleInstallFunction(prototype, "charAt", Builtins::kStringPrototypeCharAt,
                           1, true);
     SimpleInstallFunction(prototype, "charCodeAt",
                           Builtins::kStringPrototypeCharCodeAt, 1, true);
+    SimpleInstallFunction(prototype, "concat", Builtins::kStringPrototypeConcat,
+                          1, false);
     SimpleInstallFunction(prototype, "endsWith",
                           Builtins::kStringPrototypeEndsWith, 1, false);
     SimpleInstallFunction(prototype, "includes",
                           Builtins::kStringPrototypeIncludes, 1, false);
     SimpleInstallFunction(prototype, "indexOf",
                           Builtins::kStringPrototypeIndexOf, 1, false);
     SimpleInstallFunction(prototype, "lastIndexOf",
                           Builtins::kStringPrototypeLastIndexOf, 1, false);
     SimpleInstallFunction(prototype, "localeCompare",
                           Builtins::kStringPrototypeLocaleCompare, 1, true);
@@ skipping 3362 matching lines @@
 }
 
 
 // Called when the top-level V8 mutex is destroyed.
 void Bootstrapper::FreeThreadResources() {
   DCHECK(!IsActive());
 }
 
 }  // namespace internal
 }  // namespace v8