(1) StringBuilder::release should CRASH if the buffer allocation failed.
(2) Remove weird, dead code from JSString::tryGetValue, replace with an ASSERT.
(3) Move UString::createFromUTF8 out to the API, as tryCreateStringFromUTF8.
    This is only used from the API, and (now) unlike other UString::create
    methods may return UString::null() to indicate failure cases.  Better
    handle these in the API.

Reviewed by Oliver Hunt.

* API/JSClassRef.cpp:
(tryCreateStringFromUTF8):
(OpaqueJSClass::OpaqueJSClass):
(OpaqueJSClassContextData::OpaqueJSClassContextData):
* runtime/JSString.h:
(JSC::Fiber::tryGetValue):
* runtime/StringBuilder.h:
(JSC::StringBuilder::release):
* runtime/UString.cpp:
(JSC::UString::UString):
(JSC::UString::from):
(JSC::UString::find):
* runtime/UString.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@54545 268f45cc-cd09-0410-ab3c-d52691b4dbfc