[turbofan] Implement JSBuiltinReducer for String.prototype[Symbol.iterator].

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 1457 matching lines @@
     SimpleInstallFunction(prototype, "trimLeft",
                           Builtins::kStringPrototypeTrimLeft, 0, false);
     SimpleInstallFunction(prototype, "trimRight",
                           Builtins::kStringPrototypeTrimRight, 0, false);
     SimpleInstallFunction(prototype, "valueOf",
                           Builtins::kStringPrototypeValueOf, 0, true);
 
     Handle<JSFunction> iterator = SimpleCreateFunction(
         isolate, factory->NewStringFromAsciiChecked("[Symbol.iterator]"),
         Builtins::kStringPrototypeIterator, 0, true);
-    iterator->shared()->set_native(true);

[caitp, 2016/10/17 21:54:29]

I don't think we need to get rid of the set_native() call, I believe it's there
for a reason. This is done by the InstallFunction() helpers.

I __believe__ this emulates strict mode and prevents undefined/null receivers
from being converted to the global proxy (among other things), which is hit by
tests and probably causes some failures.

+    iterator->shared()->set_builtin_function_id(kStringIterator);
     JSObject::AddProperty(prototype, factory->iterator_symbol(), iterator,
                           static_cast<PropertyAttributes>(DONT_ENUM));
   }
 
   {  // --- S t r i n g I t e r a t o r ---
     Handle<JSObject> iterator_prototype(
         native_context()->initial_iterator_prototype());
 
     Handle<JSObject> string_iterator_prototype =
         factory->NewJSObject(isolate->object_function(), TENURED);
@@ skipping 2979 matching lines @@
 }
 
 
 // Called when the top-level V8 mutex is destroyed.
 void Bootstrapper::FreeThreadResources() {
   DCHECK(!IsActive());
 }
 
 }  // namespace internal
 }  // namespace v8