fourthTier: AbstractValue methods that deal with watchpoints should have access to Graph, so that in debug mode, Graph can track the history of watchpoint states and detect races
https://bugs.webkit.org/show_bug.cgi?id=115084

Reviewed by Geoffrey Garen.

The idea is that as part of https://bugs.webkit.org/show_bug.cgi?id=115083, I'll have
Graph record the initial state of a watchpoint at the time that we decide to take
advantage of it; then I will use this to disable any watchpoint-related assertions
in debug mode. Note that this "watchpoint cache" will only be maintained in debug
mode, so there will be no release performance implications. But to do this, I need to
ensure that all of the places that reason about watchpoints have access to Graph.
For example, I'll want AbstractValue::setFuturePossibleStructure to record the state
of the watchpoint in Graph so that subsequent assertions can check if the watchpoint's
state had changed since that decision was made.

* JavaScriptCore.xcodeproj/project.pbxproj:
* dfg/DFGAbstractState.cpp:
(JSC::DFG::AbstractState::initialize):
(JSC::DFG::AbstractState::executeEffects):
(JSC::DFG::AbstractState::mergeStateAtTail):
* dfg/DFGAbstractState.h:
(JSC::DFG::AbstractState::trySetConstant):
* dfg/DFGAbstractValue.cpp: Added.
(DFG):
(JSC::DFG::AbstractValue::setMostSpecific):
(JSC::DFG::AbstractValue::set):
(JSC::DFG::AbstractValue::filter):
(JSC::DFG::AbstractValue::setFuturePossibleStructure):
(JSC::DFG::AbstractValue::filterFuturePossibleStructure):
(JSC::DFG::AbstractValue::dump):
* dfg/DFGAbstractValue.h:
(DFG):
(AbstractValue):
(JSC::DFG::AbstractValue::setType):
(JSC::DFG::AbstractValue::filterByValue):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153129 268f45cc-cd09-0410-ab3c-d52691b4dbfc