[ES6] Add support for toStringTag

[ES6] Add support for toStringTag
https://bugs.webkit.org/show_bug.cgi?id=150696

Reviewed by Geoffrey Garen.

Source/JavaScriptCore:

This patch adds support for Symbol.toStringTag. This is a simple
feature, if an object passed to Object.prototype.toString() has a
toStringTag we use the tag in the string rather than the class info.
Added a test that checks this works for all the default supported classes
along with the corresponding prototype and custom cases.

* runtime/ArrayIteratorPrototype.cpp:
(JSC::ArrayIteratorPrototype::finishCreation):
* runtime/CommonIdentifiers.h:
* runtime/JSArrayBufferPrototype.cpp:
(JSC::JSArrayBufferPrototype::finishCreation):
* runtime/JSDataViewPrototype.cpp:
(JSC::JSDataViewPrototype::finishCreation):
* runtime/JSDataViewPrototype.h:
* runtime/JSModuleNamespaceObject.cpp:
(JSC::JSModuleNamespaceObject::finishCreation):
* runtime/JSONObject.cpp:
(JSC::JSONObject::finishCreation):
* runtime/JSPromisePrototype.cpp:
(JSC::JSPromisePrototype::finishCreation):
* runtime/JSTypedArrayViewPrototype.cpp:
(JSC::typedArrayViewProtoGetterFuncToStringTag):
(JSC::JSTypedArrayViewPrototype::finishCreation):
* runtime/MapIteratorPrototype.cpp:
(JSC::MapIteratorPrototype::finishCreation):
* runtime/MapPrototype.cpp:
(JSC::MapPrototype::finishCreation):
* runtime/MathObject.cpp:
(JSC::MathObject::finishCreation):
* runtime/ObjectPrototype.cpp:
(JSC::objectProtoFuncToString):
* runtime/SetIteratorPrototype.cpp:
(JSC::SetIteratorPrototype::finishCreation):
* runtime/SetPrototype.cpp:
(JSC::SetPrototype::finishCreation):
* runtime/SmallStrings.cpp:
(JSC::SmallStrings::SmallStrings):
(JSC::SmallStrings::initializeCommonStrings):
(JSC::SmallStrings::visitStrongReferences):
* runtime/SmallStrings.h:
(JSC::SmallStrings::objectStringStart):
* runtime/StringIteratorPrototype.cpp:
(JSC::StringIteratorPrototype::finishCreation):
* runtime/SymbolPrototype.cpp:
(JSC::SymbolPrototype::finishCreation):
* runtime/WeakMapPrototype.cpp:
(JSC::WeakMapPrototype::finishCreation):
* runtime/WeakSetPrototype.cpp:
(JSC::WeakSetPrototype::finishCreation):
* tests/modules/namespace.js:
* tests/stress/symbol-tostringtag.js: Added.
(toStr):
(strName):
(classes.string_appeared_here):

LayoutTests:

Symbol now has toStringTag as a member. Since Object.prototype.toString()
now does a [[Get]] on the object being stringed there are new console
error messages when accessing another window's properties.

* http/tests/history/cross-origin-replace-history-object-child-expected.txt:
* http/tests/security/cross-frame-access-custom-expected.txt:
* http/tests/security/cross-frame-access-history-get-expected.txt:
* http/tests/security/cross-frame-access-object-setPrototypeOf-expected.txt:
* js/Object-getOwnPropertyNames-expected.txt:
* js/script-tests/Object-getOwnPropertyNames.js:

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@191815 268f45cc-cd09-0410-ab3c-d52691b4dbfc