Reviewed by Oliver Hunt.

The implementation of StringImpl & UStringImpl is very similar.  Restructure
StringImpl to match UStringImpl, moving the flags and length into a base class,
so that this can be shared between both string types to increase code reuse.

* JavaScriptCore.xcodeproj/project.pbxproj:
* runtime/RopeImpl.h:
(JSC::RopeImpl::RopeImpl):
* runtime/UStringImpl.h:
(JSC::UStringImpl::UStringImpl):
* wtf/text/StringImpl.h:
(WebCore::StringImpl::StringImpl):
(WebCore::StringImpl::characters):
* wtf/text/StringImplBase.h: Copied from JavaScriptCore/runtime/UStringImpl.h.
(WTF::StringImplBase::length):
(WTF::StringImplBase::operator new):
(WTF::StringImplBase::StringImplBase):

JavaScriptGlue: Bug 37895 - Share common code from UStringImplBase with StringImpl
Add forwarding header.

Reviewed by Oliver Hunt.

* ForwardingHeaders/wtf/text/StringImplBase.h: Added.

WebCore: Bug 37895 - Share common code from UStringImplBase with StringImpl
Add forwarding header.

Reviewed by Oliver Hunt.

* ForwardingHeaders/wtf/text/StringImplBase.h: Added.



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@57932 268f45cc-cd09-0410-ab3c-d52691b4dbfc