[builtins] Migrate String.prototype.charCodeAt and String.prototype.charAt to TurboFan.

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/code-stubs.h"
 #include "src/extensions/externalize-string-extension.h"
@@ skipping 1237 matching lines @@
     PropertyAttributes attribs = static_cast<PropertyAttributes>(
         DONT_ENUM | DONT_DELETE | READ_ONLY);
     Handle<AccessorInfo> string_length(
         Accessors::StringLengthInfo(isolate, attribs));
 
     {  // Add length.
       AccessorConstantDescriptor d(factory->length_string(), string_length,
                                    attribs);
       string_map->AppendDescriptor(&d);
     }
+
+    // Create the %StringPrototype%
+    Handle<JSValue> prototype =
+        Handle<JSValue>::cast(factory->NewJSObject(string_fun, TENURED));
+    prototype->set_value(isolate->heap()->empty_string());
+    Accessors::FunctionSetPrototype(string_fun, prototype).Assert();
+
+    // 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);
   }
 
   {
     // --- S y m b o l ---
     Handle<JSObject> prototype =
         factory->NewJSObject(isolate->object_function(), TENURED);
     Handle<JSFunction> symbol_fun =
         InstallFunction(global, "Symbol", JS_VALUE_TYPE, JSValue::kSize,
                         prototype, Builtins::kSymbolConstructor);
     symbol_fun->shared()->set_construct_stub(
@@ skipping 2343 matching lines @@
 }
 
 
 // Called when the top-level V8 mutex is destroyed.
 void Bootstrapper::FreeThreadResources() {
   DCHECK(!IsActive());
 }
 
 }  // namespace internal
 }  // namespace v8