This matches WebCore::StringImpl, and better unifies behaviour throughout JSC.

Reviewed by Geoff Garen.

JavaScriptCore: 

* JavaScriptCore.exp:
* bytecode/EvalCodeCache.h:
* runtime/Identifier.cpp:
(JSC::Identifier::equal):
* runtime/Identifier.h:
* runtime/JSGlobalObjectFunctions.cpp:
(JSC::globalFuncEscape):
* runtime/JSONObject.cpp:
(JSC::gap):
(JSC::Stringifier::indent):
* runtime/NumberPrototype.cpp:
(JSC::numberProtoFuncToFixed):
(JSC::numberProtoFuncToPrecision):
* runtime/RegExp.cpp:
(JSC::RegExp::match):
* runtime/StringPrototype.cpp:
(JSC::substituteBackreferencesSlow):
(JSC::stringProtoFuncReplace):
(JSC::stringProtoFuncSplit):
(JSC::trimString):
* runtime/UString.cpp:
(JSC::UString::UString):
(JSC::UString::from):
(JSC::UString::getCString):
(JSC::UString::ascii):
(JSC::UString::operator[]):
(JSC::UString::toStrictUInt32):
(JSC::UString::find):
(JSC::UString::rfind):
(JSC::UString::substr):
(JSC::operator<):
(JSC::operator>):
(JSC::compare):
(JSC::equal):
(JSC::UString::UTF8String):
* runtime/UString.h:
(JSC::UString::size):
(JSC::operator==):
* runtime/UStringImpl.cpp:
(JSC::UStringImpl::create):
* runtime/UStringImpl.h:
(JSC::UStringImpl::create):
(JSC::UStringImpl::size):
(JSC::UStringImpl::computeHash):
(JSC::UStringImpl::UStringImpl):

WebCore: 

* bindings/js/JSDOMWindowCustom.cpp:
(WebCore::JSDOMWindow::atob):
(WebCore::JSDOMWindow::btoa):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@54789 268f45cc-cd09-0410-ab3c-d52691b4dbfc