https://bugs.webkit.org/show_bug.cgi?id=84907

Reviewed by Geoffrey Garen.

Split JSString into two classes, JSString as a base class that does not
include the fibers of a Rope, and a subclass JSRopeString that has the
rope functionality.  Both classes "share" the same ClassInfo.  Added
a bool to JSString to indicate that the string was allocated as a JSRopeString
to properly handle visiting the fiber children when the rope is resolved and
the JSRopeString appears as a JSString.  Didn't change the interface of JSString
to require any JIT changes.

As part of this change, removed "cellSize" from ClassInfo since both classes
share the same ClassInfo, but have different sizes.  The only use I could find
for cellSize was an ASSERT in allocateCell().

This appears to be neutral on performance tests.

* JavaScriptCore.vcproj/JavaScriptCore/JavaScriptCore.def: Changed JSString::resolveRope
        to JSRopeString::resolveRope
* runtime/ClassInfo.h:
(JSC):
(ClassInfo):
* runtime/JSCell.h:
(JSC::allocateCell):
* runtime/JSString.cpp:
(JSC::JSRopeString::RopeBuilder::expand):
(JSC::JSString::visitChildren):
(JSC):
(JSC::JSRopeString::visitFibers):
(JSC::JSRopeString::resolveRope):
(JSC::JSRopeString::resolveRopeSlowCase8):
(JSC::JSRopeString::resolveRopeSlowCase):
(JSC::JSRopeString::outOfMemory):
(JSC::JSRopeString::getIndexSlowCase):
* runtime/JSString.h:
(JSC):
(JSString):
(JSC::JSString::finishCreation):
(JSC::JSString::create):
(JSC::JSString::isRope):
(JSC::JSString::is8Bit):
(JSRopeString):
(RopeBuilder):
(JSC::JSRopeString::RopeBuilder::RopeBuilder):
(JSC::JSRopeString::RopeBuilder::append):
(JSC::JSRopeString::RopeBuilder::release):
(JSC::JSRopeString::RopeBuilder::length):
(JSC::JSRopeString::JSRopeString):
(JSC::JSRopeString::finishCreation):
(JSC::JSRopeString::createNull):
(JSC::JSRopeString::create):
(JSC::JSString::value):
(JSC::JSString::tryGetValue):
(JSC::JSString::getIndex):
(JSC::jsStringBuilder):
* runtime/Operations.h:
(JSC::jsString):
(JSC::jsStringFromArguments):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@115516 268f45cc-cd09-0410-ab3c-d52691b4dbfc