Reviewed by Darin.

    Reviewed by Darin.

        - discard the arguments List for an ActivationImp when the corresponding Context is destroyed (1.7% speedup)
        http://bugs.webkit.org/show_bug.cgi?id=13385

        Based an idea by Christopher E. Hyde <C.Hyde@parableuk.force9.co.uk>. His patch to do
        this also had many other List changes and I found this much simpler subset of the changes
        was actually a hair faster.

        This optimization is valid because the arguments list is only kept around to
        lazily make the arguments object. If it's not made by the time the function
        exits, it never will be, since any function that captures the continuation will
        have its own local arguments variable in scope.

        Besides the 1.7% speed improvement, it shrinks List by 4 bytes
        (which in turn shrinks ActivationImp by 4 bytes).

        * kjs/Context.cpp:
        (KJS::Context::~Context): Clear the activation's arguments list.
        * kjs/function.cpp:
        (KJS::ActivationImp::ActivationImp): Adjusted for list changes.
        (KJS::ActivationImp::mark): No need to mark, lists are always protected (this doesn't
        cause a ref-cycle for reasons stated above).
        (KJS::ActivationImp::createArgumentsObject): Clear arguments list.
        * kjs/function.h:
        * kjs/list.cpp:
        (KJS::List::List): No more needsMarking boolean
        (KJS::List::operator=): ditto
        * kjs/list.h:
        (KJS::List::List): ditto
        (KJS::List::reset): ditto
        (KJS::List::deref): ditto

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@21019 268f45cc-cd09-0410-ab3c-d52691b4dbfc