Reviewed by Oliver Hunt.

JavaScriptCore: 

* API/JSClassRef.cpp:
(OpaqueJSClass::~OpaqueJSClass): Classname may be null/empty, and these are an identifer.  This is okay, since the null/empty strings are shared across all threads.
* JavaScriptCore.exp:
* runtime/Identifier.cpp:
(JSC::Identifier::add): No need to explicitly hash null reps, this is done in the ststic UStringImpl constructor.
(JSC::Identifier::addSlowCase): UStringImpl::empty() handled & checkCurrentIdentifierTable now called in the header.
(JSC::Identifier::checkCurrentIdentifierTable): Replaces checkSameIdentifierTable (this no longer checked the rep since the identifierTable pointer was removed from UString::Rep long ago).
* runtime/Identifier.h:
(JSC::Identifier::add): Replace call to checkSameIdentifierTable with call to checkCurrentIdentifierTable at head of function.
* runtime/UStringImpl.cpp:
(JSC::UStringImpl::~UStringImpl): Remove call to checkConsistency - this function no longer checks anything interesting.
* runtime/UStringImpl.h:
(JSC::UStringOrRopeImpl::UStringOrRopeImpl): Set s_refCountFlagIsIdentifier in static constructor.
(JSC::UStringImpl::UStringImpl): remove calls to checkConsistency (see above), add new ASSERT to substring constructor.
(JSC::UStringImpl::setHash): ASSERT not static (static strings set the hash in their constructor, should not reach this code path).
(JSC::UStringImpl::create): Add missing ASSERT.
(JSC::UStringImpl::setIsIdentifier): ASSERT !isStatic() (static strings hash set in constructor).

WebCore: 

* platform/text/StringImpl.cpp:
(WebCore::StringImpl::~StringImpl): Add ASSERT
(WebCore::StringImpl::sharedBuffer): Add ASSERT
* platform/text/StringImpl.h:
(WebCore::StringImpl::setHash): Add ASSERT
(WebCore::StringImpl::isStatic): added.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@55943 268f45cc-cd09-0410-ab3c-d52691b4dbfc